[PATCH v5 0/2] KEYS: Read keys to internal buffer & then copy to userspace

[PATCH v5 0/2] KEYS: Read keys to internal buffer & then copy to userspace

[Waiman Long]

v5:
 - Merge v4 patches 2 and 3 into 1 to avoid sparse warning. Merge some of 
   commit logs into patch 1 as well. There is no further change.

v4:
 - Remove the __user annotation from big_key_read() and user_read() in
   patch 1.
 - Add a new patch 2 to remove __user annotation from rxrpc_read().
 - Add a new patch 3 to remove __user annotation from dns_resolver_read().
 - Merge the original patches 2 and 3 into a single patch 4 and refactor
   it as suggested by Jarkko and Eric.

v3:
 - Reorganize the keyctl_read_key() code to make it more readable as
   suggested by Jarkko Sakkinen.
 - Add patch 3 to use kvmalloc() for safer large buffer allocation as
   suggested by David Howells.

v2:
 - Handle NULL buffer and buflen properly in patch 1.
 - Fix a bug in big_key.c.
 - Add patch 2 to handle arbitrary large user-supplied buflen.

The current security key read methods are called with the key semaphore
held.  The methods then copy out the key data to userspace which is
subjected to page fault and may acquire the mmap semaphore. That can
result in circular lock dependency and hence a chance to get into
deadlock.

To avoid such a deadlock, an internal buffer is now allocated for getting
out the necessary data first. After releasing the key semaphore, the
key data are then copied out to userspace sidestepping the circular
lock dependency.

The keyutils test suite was run and the test passed with these patchset
applied without any falure.

Waiman Long (2):
  KEYS: Don't write out to userspace while holding key semaphore
  KEYS: Avoid false positive ENOMEM error on key read

 include/keys/big_key-type.h               |  2 +-
 include/keys/user-type.h                  |  3 +-
 include/linux/key-type.h                  |  2 +-
 net/dns_resolver/dns_key.c                |  2 +-
 net/rxrpc/key.c                           | 27 +++----
 security/keys/big_key.c                   | 11 ++-
 security/keys/encrypted-keys/encrypted.c  |  7 +-
 security/keys/internal.h                  | 12 ++++
 security/keys/keyctl.c                    | 86 ++++++++++++++++++++---
 security/keys/keyring.c                   |  6 +-
 security/keys/request_key_auth.c          |  7 +-
 security/keys/trusted-keys/trusted_tpm1.c | 14 +---
 security/keys/user_defined.c              |  5 +-
 13 files changed, 116 insertions(+), 68 deletions(-)

-- 
2.18.1

[PATCH v5 0/2] KEYS: Read keys to internal buffer & then copy to userspace

[Waiman Long]

v5:
 - Merge v4 patches 2 and 3 into 1 to avoid sparse warning. Merge some of 
   commit logs into patch 1 as well. There is no further change.

v4:
 - Remove the __user annotation from big_key_read() and user_read() in
   patch 1.
 - Add a new patch 2 to remove __user annotation from rxrpc_read().
 - Add a new patch 3 to remove __user annotation from dns_resolver_read().
 - Merge the original patches 2 and 3 into a single patch 4 and refactor
   it as suggested by Jarkko and Eric.

v3:
 - Reorganize the keyctl_read_key() code to make it more readable as
   suggested by Jarkko Sakkinen.
 - Add patch 3 to use kvmalloc() for safer large buffer allocation as
   suggested by David Howells.

v2:
 - Handle NULL buffer and buflen properly in patch 1.
 - Fix a bug in big_key.c.
 - Add patch 2 to handle arbitrary large user-supplied buflen.

The current security key read methods are called with the key semaphore
held.  The methods then copy out the key data to userspace which is
subjected to page fault and may acquire the mmap semaphore. That can
result in circular lock dependency and hence a chance to get into
deadlock.

To avoid such a deadlock, an internal buffer is now allocated for getting
out the necessary data first. After releasing the key semaphore, the
key data are then copied out to userspace sidestepping the circular
lock dependency.

The keyutils test suite was run and the test passed with these patchset
applied without any falure.

Waiman Long (2):
  KEYS: Don't write out to userspace while holding key semaphore
  KEYS: Avoid false positive ENOMEM error on key read

 include/keys/big_key-type.h               |  2 +-
 include/keys/user-type.h                  |  3 +-
 include/linux/key-type.h                  |  2 +-
 net/dns_resolver/dns_key.c                |  2 +-
 net/rxrpc/key.c                           | 27 +++----
 security/keys/big_key.c                   | 11 ++-
 security/keys/encrypted-keys/encrypted.c  |  7 +-
 security/keys/internal.h                  | 12 ++++
 security/keys/keyctl.c                    | 86 ++++++++++++++++++++---
 security/keys/keyring.c                   |  6 +-
 security/keys/request_key_auth.c          |  7 +-
 security/keys/trusted-keys/trusted_tpm1.c | 14 +---
 security/keys/user_defined.c              |  5 +-
 13 files changed, 116 insertions(+), 68 deletions(-)

-- 
2.18.1

[PATCH v5 1/2] KEYS: Don't write out to userspace while holding key semaphore

[Waiman Long]

A lockdep circular locking dependency report was seen when running a
keyutils test:

[12537.027242] ===========================
[12537.059309] WARNING: possible circular locking dependency detected
[12537.088148] 4.18.0-147.7.1.el8_1.x86_64+debug #1 Tainted: G OE    --------- -  -
[12537.125253] ------------------------------------------------------
[12537.153189] keyctl/25598 is trying to acquire lock:
[12537.175087] 000000007c39f96c (&mm->mmap_sem){++++}, at: __might_fault+0xc4/0x1b0
[12537.208365]
[12537.208365] but task is already holding lock:
[12537.234507] 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12537.270476]
[12537.270476] which lock already depends on the new lock.
[12537.270476]
[12537.307209]
[12537.307209] the existing dependency chain (in reverse order) is:
[12537.340754]
[12537.340754] -> #3 (&type->lock_class){++++}:
[12537.367434]        down_write+0x4d/0x110
[12537.385202]        __key_link_begin+0x87/0x280
[12537.405232]        request_key_and_link+0x483/0xf70
[12537.427221]        request_key+0x3c/0x80
[12537.444839]        dns_query+0x1db/0x5a5 [dns_resolver]
[12537.468445]        dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.496731]        cifs_reconnect+0xe04/0x2500 [cifs]
[12537.519418]        cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.546263]        cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.573551]        cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.601045]        kthread+0x30c/0x3d0
[12537.617906]        ret_from_fork+0x3a/0x50
[12537.636225]
[12537.636225] -> #2 (root_key_user.cons_lock){+.+.}:
[12537.664525]        __mutex_lock+0x105/0x11f0
[12537.683734]        request_key_and_link+0x35a/0xf70
[12537.705640]        request_key+0x3c/0x80
[12537.723304]        dns_query+0x1db/0x5a5 [dns_resolver]
[12537.746773]        dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.775607]        cifs_reconnect+0xe04/0x2500 [cifs]
[12537.798322]        cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.823369]        cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.847262]        cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.873477]        kthread+0x30c/0x3d0
[12537.890281]        ret_from_fork+0x3a/0x50
[12537.908649]
[12537.908649] -> #1 (&tcp_ses->srv_mutex){+.+.}:
[12537.935225]        __mutex_lock+0x105/0x11f0
[12537.954450]        cifs_call_async+0x102/0x7f0 [cifs]
[12537.977250]        smb2_async_readv+0x6c3/0xc90 [cifs]
[12538.000659]        cifs_readpages+0x120a/0x1e50 [cifs]
[12538.023920]        read_pages+0xf5/0x560
[12538.041583]        __do_page_cache_readahead+0x41d/0x4b0
[12538.067047]        ondemand_readahead+0x44c/0xc10
[12538.092069]        filemap_fault+0xec1/0x1830
[12538.111637]        __do_fault+0x82/0x260
[12538.129216]        do_fault+0x419/0xfb0
[12538.146390]        __handle_mm_fault+0x862/0xdf0
[12538.167408]        handle_mm_fault+0x154/0x550
[12538.187401]        __do_page_fault+0x42f/0xa60
[12538.207395]        do_page_fault+0x38/0x5e0
[12538.225777]        page_fault+0x1e/0x30
[12538.243010]
[12538.243010] -> #0 (&mm->mmap_sem){++++}:
[12538.267875]        lock_acquire+0x14c/0x420
[12538.286848]        __might_fault+0x119/0x1b0
[12538.306006]        keyring_read_iterator+0x7e/0x170
[12538.327936]        assoc_array_subtree_iterate+0x97/0x280
[12538.352154]        keyring_read+0xe9/0x110
[12538.370558]        keyctl_read_key+0x1b9/0x220
[12538.391470]        do_syscall_64+0xa5/0x4b0
[12538.410511]        entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[12538.435535]
[12538.435535] other info that might help us debug this:
[12538.435535]
[12538.472829] Chain exists of:
[12538.472829]   &mm->mmap_sem --> root_key_user.cons_lock --> &type->lock_class
[12538.472829]
[12538.524820]  Possible unsafe locking scenario:
[12538.524820]
[12538.551431]        CPU0                    CPU1
[12538.572654]        ----                    ----
[12538.595865]   lock(&type->lock_class);
[12538.613737]                                lock(root_key_user.cons_lock);
[12538.644234]                                lock(&type->lock_class);
[12538.672410]   lock(&mm->mmap_sem);
[12538.687758]
[12538.687758]  *** DEADLOCK ***
[12538.687758]
[12538.714455] 1 lock held by keyctl/25598:
[12538.732097]  #0: 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12538.770573]
[12538.770573] stack backtrace:
[12538.790136] CPU: 2 PID: 25598 Comm: keyctl Kdump: loaded Tainted: G
[12538.844855] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 12/27/2015
[12538.881963] Call Trace:
[12538.892897]  dump_stack+0x9a/0xf0
[12538.907908]  print_circular_bug.isra.25.cold.50+0x1bc/0x279
[12538.932891]  ? save_trace+0xd6/0x250
[12538.948979]  check_prev_add.constprop.32+0xc36/0x14f0
[12538.971643]  ? keyring_compare_object+0x104/0x190
[12538.992738]  ? check_usage+0x550/0x550
[12539.009845]  ? sched_clock+0x5/0x10
[12539.025484]  ? sched_clock_cpu+0x18/0x1e0
[12539.043555]  __lock_acquire+0x1f12/0x38d0
[12539.061551]  ? trace_hardirqs_on+0x10/0x10
[12539.080554]  lock_acquire+0x14c/0x420
[12539.100330]  ? __might_fault+0xc4/0x1b0
[12539.119079]  __might_fault+0x119/0x1b0
[12539.135869]  ? __might_fault+0xc4/0x1b0
[12539.153234]  keyring_read_iterator+0x7e/0x170
[12539.172787]  ? keyring_read+0x110/0x110
[12539.190059]  assoc_array_subtree_iterate+0x97/0x280
[12539.211526]  keyring_read+0xe9/0x110
[12539.227561]  ? keyring_gc_check_iterator+0xc0/0xc0
[12539.249076]  keyctl_read_key+0x1b9/0x220
[12539.266660]  do_syscall_64+0xa5/0x4b0
[12539.283091]  entry_SYSCALL_64_after_hwframe+0x6a/0xdf

One way to prevent this deadlock scenario from happening is to not
allow writing to userspace while holding the key semaphore. Instead,
an internal buffer is allocated for getting the keys out from the
read method first before copying them out to userspace without holding
the lock.

That requires taking out the __user modifier from all the relevant
read methods as well as additional changes to not use any userspace
write helpers. That is,

  1) The put_user() call is replaced by a direct copy.
  2) The copy_to_user() call is replaced by memcpy().
  3) All the fault handling code is removed.

Compiling on a x86-64 system, the size of the rxrpc_read() function is
reduced from 3795 bytes to 2384 bytes with this patch.

Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/keys/big_key-type.h               |  2 +-
 include/keys/user-type.h                  |  3 +-
 include/linux/key-type.h                  |  2 +-
 net/dns_resolver/dns_key.c                |  2 +-
 net/rxrpc/key.c                           | 27 ++++-------
 security/keys/big_key.c                   | 11 ++---
 security/keys/encrypted-keys/encrypted.c  |  7 ++-
 security/keys/keyctl.c                    | 57 +++++++++++++++++++----
 security/keys/keyring.c                   |  6 +--
 security/keys/request_key_auth.c          |  7 ++-
 security/keys/trusted-keys/trusted_tpm1.c | 14 +-----
 security/keys/user_defined.c              |  5 +-
 12 files changed, 77 insertions(+), 66 deletions(-)

diff --git a/include/keys/big_key-type.h b/include/keys/big_key-type.h
index f6a7ba4dccd4..3fee04f81439 100644
--- a/include/keys/big_key-type.h
+++ b/include/keys/big_key-type.h
@@ -17,6 +17,6 @@ extern void big_key_free_preparse(struct key_preparsed_payload *prep);
 extern void big_key_revoke(struct key *key);
 extern void big_key_destroy(struct key *key);
 extern void big_key_describe(const struct key *big_key, struct seq_file *m);
-extern long big_key_read(const struct key *key, char __user *buffer, size_t buflen);
+extern long big_key_read(const struct key *key, char *buffer, size_t buflen);
 
 #endif /* _KEYS_BIG_KEY_TYPE_H */
diff --git a/include/keys/user-type.h b/include/keys/user-type.h
index d5e73266a81a..be61fcddc02a 100644
--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -41,8 +41,7 @@ extern int user_update(struct key *key, struct key_preparsed_payload *prep);
 extern void user_revoke(struct key *key);
 extern void user_destroy(struct key *key);
 extern void user_describe(const struct key *user, struct seq_file *m);
-extern long user_read(const struct key *key,
-		      char __user *buffer, size_t buflen);
+extern long user_read(const struct key *key, char *buffer, size_t buflen);
 
 static inline const struct user_key_payload *user_key_payload_rcu(const struct key *key)
 {
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 4ded94bcf274..2ab2d6d6aeab 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -127,7 +127,7 @@ struct key_type {
 	 *   much is copied into the buffer
 	 * - shouldn't do the copy if the buffer is NULL
 	 */
-	long (*read)(const struct key *key, char __user *buffer, size_t buflen);
+	long (*read)(const struct key *key, char *buffer, size_t buflen);
 
 	/* handle request_key() for this type instead of invoking
 	 * /sbin/request-key (optional)
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 3e1a90669006..ad53eb31d40f 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -302,7 +302,7 @@ static void dns_resolver_describe(const struct key *key, struct seq_file *m)
  * - the key's semaphore is read-locked
  */
 static long dns_resolver_read(const struct key *key,
-			      char __user *buffer, size_t buflen)
+			      char *buffer, size_t buflen)
 {
 	int err = PTR_ERR(key->payload.data[dns_key_error]);
 
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 6c3f35fac42d..0c98313dd7a8 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -31,7 +31,7 @@ static void rxrpc_free_preparse_s(struct key_preparsed_payload *);
 static void rxrpc_destroy(struct key *);
 static void rxrpc_destroy_s(struct key *);
 static void rxrpc_describe(const struct key *, struct seq_file *);
-static long rxrpc_read(const struct key *, char __user *, size_t);
+static long rxrpc_read(const struct key *, char *, size_t);
 
 /*
  * rxrpc defined keys take an arbitrary string as the description and an
@@ -1042,12 +1042,12 @@ EXPORT_SYMBOL(rxrpc_get_null_key);
  * - this returns the result in XDR form
  */
 static long rxrpc_read(const struct key *key,
-		       char __user *buffer, size_t buflen)
+		       char *buffer, size_t buflen)
 {
 	const struct rxrpc_key_token *token;
 	const struct krb5_principal *princ;
 	size_t size;
-	__be32 __user *xdr, *oldxdr;
+	__be32 *xdr, *oldxdr;
 	u32 cnlen, toksize, ntoks, tok, zero;
 	u16 toksizes[AFSTOKEN_MAX];
 	int loop;
@@ -1124,30 +1124,25 @@ static long rxrpc_read(const struct key *key,
 	if (!buffer || buflen < size)
 		return size;
 
-	xdr = (__be32 __user *) buffer;
+	xdr = (__be32 *)buffer;
 	zero = 0;
 #define ENCODE(x)				\
 	do {					\
-		__be32 y = htonl(x);		\
-		if (put_user(y, xdr++) < 0)	\
-			goto fault;		\
+		*xdr++ = htonl(x);		\
 	} while(0)
 #define ENCODE_DATA(l, s)						\
 	do {								\
 		u32 _l = (l);						\
 		ENCODE(l);						\
-		if (copy_to_user(xdr, (s), _l) != 0)			\
-			goto fault;					\
-		if (_l & 3 &&						\
-		    copy_to_user((u8 __user *)xdr + _l, &zero, 4 - (_l & 3)) != 0) \
-			goto fault;					\
+		memcpy(xdr, (s), _l);					\
+		if (_l & 3)						\
+			memcpy((u8 *)xdr + _l, &zero, 4 - (_l & 3));	\
 		xdr += (_l + 3) >> 2;					\
 	} while(0)
 #define ENCODE64(x)					\
 	do {						\
 		__be64 y = cpu_to_be64(x);		\
-		if (copy_to_user(xdr, &y, 8) != 0)	\
-			goto fault;			\
+		memcpy(xdr, &y, 8);			\
 		xdr += 8 >> 2;				\
 	} while(0)
 #define ENCODE_STR(s)				\
@@ -1238,8 +1233,4 @@ static long rxrpc_read(const struct key *key,
 	ASSERTCMP((char __user *) xdr - buffer, =, size);
 	_leave(" = %zu", size);
 	return size;
-
-fault:
-	_leave(" = -EFAULT");
-	return -EFAULT;
 }
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index 001abe530a0d..82008f900930 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -352,7 +352,7 @@ void big_key_describe(const struct key *key, struct seq_file *m)
  * read the key data
  * - the key's semaphore is read-locked
  */
-long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
+long big_key_read(const struct key *key, char *buffer, size_t buflen)
 {
 	size_t datalen = (size_t)key->payload.data[big_key_len];
 	long ret;
@@ -391,9 +391,8 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 
 		ret = datalen;
 
-		/* copy decrypted data to user */
-		if (copy_to_user(buffer, buf->virt, datalen) != 0)
-			ret = -EFAULT;
+		/* copy out decrypted data */
+		memcpy(buffer, buf->virt, datalen);
 
 err_fput:
 		fput(file);
@@ -401,9 +400,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 		big_key_free_buffer(buf);
 	} else {
 		ret = datalen;
-		if (copy_to_user(buffer, key->payload.data[big_key_data],
-				 datalen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, key->payload.data[big_key_data], datalen);
 	}
 
 	return ret;
diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 60720f58cbe0..f6797ba44bf7 100644
--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -902,14 +902,14 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
 }
 
 /*
- * encrypted_read - format and copy the encrypted data to userspace
+ * encrypted_read - format and copy out the encrypted data
  *
  * The resulting datablob format is:
  * <master-key name> <decrypted data length> <encrypted iv> <encrypted data>
  *
  * On success, return to userspace the encrypted key datablob size.
  */
-static long encrypted_read(const struct key *key, char __user *buffer,
+static long encrypted_read(const struct key *key, char *buffer,
 			   size_t buflen)
 {
 	struct encrypted_key_payload *epayload;
@@ -957,8 +957,7 @@ static long encrypted_read(const struct key *key, char __user *buffer,
 	key_put(mkey);
 	memzero_explicit(derived_key, sizeof(derived_key));
 
-	if (copy_to_user(buffer, ascii_buf, asciiblob_len) != 0)
-		ret = -EFAULT;
+	memcpy(buffer, ascii_buf, asciiblob_len);
 	kzfree(ascii_buf);
 
 	return asciiblob_len;
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 9b898c969558..81f68e434b9f 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -797,6 +797,21 @@ long keyctl_keyring_search(key_serial_t ringid,
 	return ret;
 }
 
+/*
+ * Call the read method
+ */
+static long __keyctl_read_key(struct key *key, char *buffer, size_t buflen)
+{
+	long ret;
+
+	down_read(&key->sem);
+	ret = key_validate(key);
+	if (ret = 0)
+		ret = key->type->read(key, buffer, buflen);
+	up_read(&key->sem);
+	return ret;
+}
+
 /*
  * Read a key's payload.
  *
@@ -844,16 +859,42 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 
 	/* the key is probably readable - now try to read it */
 can_read_key:
-	ret = -EOPNOTSUPP;
-	if (key->type->read) {
-		/* Read the data with the semaphore held (since we might sleep)
+	if (!key->type->read) {
+		ret = -EOPNOTSUPP;
+		goto error2;
+	}
+
+	if (!buffer || !buflen) {
+		/* Get the key length from the read method */
+		ret = __keyctl_read_key(key, NULL, 0);
+	} else {
+
+		/*
+		 * Read the data with the semaphore held (since we might sleep)
 		 * to protect against the key being updated or revoked.
+		 *
+		 * Allocating a temporary buffer to hold the keys before
+		 * transferring them to user buffer to avoid potential
+		 * deadlock involving page fault and mmap_sem.
+		 */
+		char *tmpbuf = kmalloc(buflen, GFP_KERNEL);
+
+		if (!tmpbuf) {
+			ret = -ENOMEM;
+			goto error2;
+		}
+		ret = __keyctl_read_key(key, tmpbuf, buflen);
+
+		/*
+		 * Read methods will just return the required length
+		 * without any copying if the provided length isn't big
+		 * enough.
 		 */
-		down_read(&key->sem);
-		ret = key_validate(key);
-		if (ret = 0)
-			ret = key->type->read(key, buffer, buflen);
-		up_read(&key->sem);
+		if ((ret > 0) && (ret <= buflen)) {
+			if (copy_to_user(buffer, tmpbuf, ret))
+				ret = -EFAULT;
+		}
+		kzfree(tmpbuf);
 	}
 
 error2:
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index febf36c6ddc5..5ca620d31cd3 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -459,7 +459,6 @@ static int keyring_read_iterator(const void *object, void *data)
 {
 	struct keyring_read_iterator_context *ctx = data;
 	const struct key *key = keyring_ptr_to_key(object);
-	int ret;
 
 	kenter("{%s,%d},,{%zu/%zu}",
 	       key->type->name, key->serial, ctx->count, ctx->buflen);
@@ -467,10 +466,7 @@ static int keyring_read_iterator(const void *object, void *data)
 	if (ctx->count >= ctx->buflen)
 		return 1;
 
-	ret = put_user(key->serial, ctx->buffer);
-	if (ret < 0)
-		return ret;
-	ctx->buffer++;
+	*ctx->buffer++ = key->serial;
 	ctx->count += sizeof(key->serial);
 	return 0;
 }
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index ecba39c93fd9..41e9735006d0 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -22,7 +22,7 @@ static int request_key_auth_instantiate(struct key *,
 static void request_key_auth_describe(const struct key *, struct seq_file *);
 static void request_key_auth_revoke(struct key *);
 static void request_key_auth_destroy(struct key *);
-static long request_key_auth_read(const struct key *, char __user *, size_t);
+static long request_key_auth_read(const struct key *, char *, size_t);
 
 /*
  * The request-key authorisation key type definition.
@@ -80,7 +80,7 @@ static void request_key_auth_describe(const struct key *key,
  * - the key's semaphore is read-locked
  */
 static long request_key_auth_read(const struct key *key,
-				  char __user *buffer, size_t buflen)
+				  char *buffer, size_t buflen)
 {
 	struct request_key_auth *rka = dereference_key_locked(key);
 	size_t datalen;
@@ -97,8 +97,7 @@ static long request_key_auth_read(const struct key *key,
 		if (buflen > datalen)
 			buflen = datalen;
 
-		if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, rka->callout_info, buflen);
 	}
 
 	return ret;
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index d2c5ec1e040b..8001ab07e63b 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -1130,11 +1130,10 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
  * trusted_read - copy the sealed blob data to userspace in hex.
  * On success, return to userspace the trusted key datablob size.
  */
-static long trusted_read(const struct key *key, char __user *buffer,
+static long trusted_read(const struct key *key, char *buffer,
 			 size_t buflen)
 {
 	const struct trusted_key_payload *p;
-	char *ascii_buf;
 	char *bufp;
 	int i;
 
@@ -1143,18 +1142,9 @@ static long trusted_read(const struct key *key, char __user *buffer,
 		return -EINVAL;
 
 	if (buffer && buflen >= 2 * p->blob_len) {
-		ascii_buf = kmalloc_array(2, p->blob_len, GFP_KERNEL);
-		if (!ascii_buf)
-			return -ENOMEM;
-
-		bufp = ascii_buf;
+		bufp = buffer;
 		for (i = 0; i < p->blob_len; i++)
 			bufp = hex_byte_pack(bufp, p->blob[i]);
-		if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) {
-			kzfree(ascii_buf);
-			return -EFAULT;
-		}
-		kzfree(ascii_buf);
 	}
 	return 2 * p->blob_len;
 }
diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 6f12de4ce549..07d4287e9084 100644
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -168,7 +168,7 @@ EXPORT_SYMBOL_GPL(user_describe);
  * read the key data
  * - the key's semaphore is read-locked
  */
-long user_read(const struct key *key, char __user *buffer, size_t buflen)
+long user_read(const struct key *key, char *buffer, size_t buflen)
 {
 	const struct user_key_payload *upayload;
 	long ret;
@@ -181,8 +181,7 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen)
 		if (buflen > upayload->datalen)
 			buflen = upayload->datalen;
 
-		if (copy_to_user(buffer, upayload->data, buflen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, upayload->data, buflen);
 	}
 
 	return ret;
-- 
2.18.1

[PATCH v5 1/2] KEYS: Don't write out to userspace while holding key semaphore

[Waiman Long]

A lockdep circular locking dependency report was seen when running a
keyutils test:

[12537.027242] ======================================================
[12537.059309] WARNING: possible circular locking dependency detected
[12537.088148] 4.18.0-147.7.1.el8_1.x86_64+debug #1 Tainted: G OE    --------- -  -
[12537.125253] ------------------------------------------------------
[12537.153189] keyctl/25598 is trying to acquire lock:
[12537.175087] 000000007c39f96c (&mm->mmap_sem){++++}, at: __might_fault+0xc4/0x1b0
[12537.208365]
[12537.208365] but task is already holding lock:
[12537.234507] 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12537.270476]
[12537.270476] which lock already depends on the new lock.
[12537.270476]
[12537.307209]
[12537.307209] the existing dependency chain (in reverse order) is:
[12537.340754]
[12537.340754] -> #3 (&type->lock_class){++++}:
[12537.367434]        down_write+0x4d/0x110
[12537.385202]        __key_link_begin+0x87/0x280
[12537.405232]        request_key_and_link+0x483/0xf70
[12537.427221]        request_key+0x3c/0x80
[12537.444839]        dns_query+0x1db/0x5a5 [dns_resolver]
[12537.468445]        dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.496731]        cifs_reconnect+0xe04/0x2500 [cifs]
[12537.519418]        cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.546263]        cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.573551]        cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.601045]        kthread+0x30c/0x3d0
[12537.617906]        ret_from_fork+0x3a/0x50
[12537.636225]
[12537.636225] -> #2 (root_key_user.cons_lock){+.+.}:
[12537.664525]        __mutex_lock+0x105/0x11f0
[12537.683734]        request_key_and_link+0x35a/0xf70
[12537.705640]        request_key+0x3c/0x80
[12537.723304]        dns_query+0x1db/0x5a5 [dns_resolver]
[12537.746773]        dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.775607]        cifs_reconnect+0xe04/0x2500 [cifs]
[12537.798322]        cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.823369]        cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.847262]        cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.873477]        kthread+0x30c/0x3d0
[12537.890281]        ret_from_fork+0x3a/0x50
[12537.908649]
[12537.908649] -> #1 (&tcp_ses->srv_mutex){+.+.}:
[12537.935225]        __mutex_lock+0x105/0x11f0
[12537.954450]        cifs_call_async+0x102/0x7f0 [cifs]
[12537.977250]        smb2_async_readv+0x6c3/0xc90 [cifs]
[12538.000659]        cifs_readpages+0x120a/0x1e50 [cifs]
[12538.023920]        read_pages+0xf5/0x560
[12538.041583]        __do_page_cache_readahead+0x41d/0x4b0
[12538.067047]        ondemand_readahead+0x44c/0xc10
[12538.092069]        filemap_fault+0xec1/0x1830
[12538.111637]        __do_fault+0x82/0x260
[12538.129216]        do_fault+0x419/0xfb0
[12538.146390]        __handle_mm_fault+0x862/0xdf0
[12538.167408]        handle_mm_fault+0x154/0x550
[12538.187401]        __do_page_fault+0x42f/0xa60
[12538.207395]        do_page_fault+0x38/0x5e0
[12538.225777]        page_fault+0x1e/0x30
[12538.243010]
[12538.243010] -> #0 (&mm->mmap_sem){++++}:
[12538.267875]        lock_acquire+0x14c/0x420
[12538.286848]        __might_fault+0x119/0x1b0
[12538.306006]        keyring_read_iterator+0x7e/0x170
[12538.327936]        assoc_array_subtree_iterate+0x97/0x280
[12538.352154]        keyring_read+0xe9/0x110
[12538.370558]        keyctl_read_key+0x1b9/0x220
[12538.391470]        do_syscall_64+0xa5/0x4b0
[12538.410511]        entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[12538.435535]
[12538.435535] other info that might help us debug this:
[12538.435535]
[12538.472829] Chain exists of:
[12538.472829]   &mm->mmap_sem --> root_key_user.cons_lock --> &type->lock_class
[12538.472829]
[12538.524820]  Possible unsafe locking scenario:
[12538.524820]
[12538.551431]        CPU0                    CPU1
[12538.572654]        ----                    ----
[12538.595865]   lock(&type->lock_class);
[12538.613737]                                lock(root_key_user.cons_lock);
[12538.644234]                                lock(&type->lock_class);
[12538.672410]   lock(&mm->mmap_sem);
[12538.687758]
[12538.687758]  *** DEADLOCK ***
[12538.687758]
[12538.714455] 1 lock held by keyctl/25598:
[12538.732097]  #0: 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12538.770573]
[12538.770573] stack backtrace:
[12538.790136] CPU: 2 PID: 25598 Comm: keyctl Kdump: loaded Tainted: G
[12538.844855] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 12/27/2015
[12538.881963] Call Trace:
[12538.892897]  dump_stack+0x9a/0xf0
[12538.907908]  print_circular_bug.isra.25.cold.50+0x1bc/0x279
[12538.932891]  ? save_trace+0xd6/0x250
[12538.948979]  check_prev_add.constprop.32+0xc36/0x14f0
[12538.971643]  ? keyring_compare_object+0x104/0x190
[12538.992738]  ? check_usage+0x550/0x550
[12539.009845]  ? sched_clock+0x5/0x10
[12539.025484]  ? sched_clock_cpu+0x18/0x1e0
[12539.043555]  __lock_acquire+0x1f12/0x38d0
[12539.061551]  ? trace_hardirqs_on+0x10/0x10
[12539.080554]  lock_acquire+0x14c/0x420
[12539.100330]  ? __might_fault+0xc4/0x1b0
[12539.119079]  __might_fault+0x119/0x1b0
[12539.135869]  ? __might_fault+0xc4/0x1b0
[12539.153234]  keyring_read_iterator+0x7e/0x170
[12539.172787]  ? keyring_read+0x110/0x110
[12539.190059]  assoc_array_subtree_iterate+0x97/0x280
[12539.211526]  keyring_read+0xe9/0x110
[12539.227561]  ? keyring_gc_check_iterator+0xc0/0xc0
[12539.249076]  keyctl_read_key+0x1b9/0x220
[12539.266660]  do_syscall_64+0xa5/0x4b0
[12539.283091]  entry_SYSCALL_64_after_hwframe+0x6a/0xdf

One way to prevent this deadlock scenario from happening is to not
allow writing to userspace while holding the key semaphore. Instead,
an internal buffer is allocated for getting the keys out from the
read method first before copying them out to userspace without holding
the lock.

That requires taking out the __user modifier from all the relevant
read methods as well as additional changes to not use any userspace
write helpers. That is,

  1) The put_user() call is replaced by a direct copy.
  2) The copy_to_user() call is replaced by memcpy().
  3) All the fault handling code is removed.

Compiling on a x86-64 system, the size of the rxrpc_read() function is
reduced from 3795 bytes to 2384 bytes with this patch.

Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/keys/big_key-type.h               |  2 +-
 include/keys/user-type.h                  |  3 +-
 include/linux/key-type.h                  |  2 +-
 net/dns_resolver/dns_key.c                |  2 +-
 net/rxrpc/key.c                           | 27 ++++-------
 security/keys/big_key.c                   | 11 ++---
 security/keys/encrypted-keys/encrypted.c  |  7 ++-
 security/keys/keyctl.c                    | 57 +++++++++++++++++++----
 security/keys/keyring.c                   |  6 +--
 security/keys/request_key_auth.c          |  7 ++-
 security/keys/trusted-keys/trusted_tpm1.c | 14 +-----
 security/keys/user_defined.c              |  5 +-
 12 files changed, 77 insertions(+), 66 deletions(-)

diff --git a/include/keys/big_key-type.h b/include/keys/big_key-type.h
index f6a7ba4dccd4..3fee04f81439 100644
--- a/include/keys/big_key-type.h
+++ b/include/keys/big_key-type.h
@@ -17,6 +17,6 @@ extern void big_key_free_preparse(struct key_preparsed_payload *prep);
 extern void big_key_revoke(struct key *key);
 extern void big_key_destroy(struct key *key);
 extern void big_key_describe(const struct key *big_key, struct seq_file *m);
-extern long big_key_read(const struct key *key, char __user *buffer, size_t buflen);
+extern long big_key_read(const struct key *key, char *buffer, size_t buflen);
 
 #endif /* _KEYS_BIG_KEY_TYPE_H */
diff --git a/include/keys/user-type.h b/include/keys/user-type.h
index d5e73266a81a..be61fcddc02a 100644
--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -41,8 +41,7 @@ extern int user_update(struct key *key, struct key_preparsed_payload *prep);
 extern void user_revoke(struct key *key);
 extern void user_destroy(struct key *key);
 extern void user_describe(const struct key *user, struct seq_file *m);
-extern long user_read(const struct key *key,
-		      char __user *buffer, size_t buflen);
+extern long user_read(const struct key *key, char *buffer, size_t buflen);
 
 static inline const struct user_key_payload *user_key_payload_rcu(const struct key *key)
 {
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index 4ded94bcf274..2ab2d6d6aeab 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -127,7 +127,7 @@ struct key_type {
 	 *   much is copied into the buffer
 	 * - shouldn't do the copy if the buffer is NULL
 	 */
-	long (*read)(const struct key *key, char __user *buffer, size_t buflen);
+	long (*read)(const struct key *key, char *buffer, size_t buflen);
 
 	/* handle request_key() for this type instead of invoking
 	 * /sbin/request-key (optional)
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 3e1a90669006..ad53eb31d40f 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -302,7 +302,7 @@ static void dns_resolver_describe(const struct key *key, struct seq_file *m)
  * - the key's semaphore is read-locked
  */
 static long dns_resolver_read(const struct key *key,
-			      char __user *buffer, size_t buflen)
+			      char *buffer, size_t buflen)
 {
 	int err = PTR_ERR(key->payload.data[dns_key_error]);
 
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 6c3f35fac42d..0c98313dd7a8 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -31,7 +31,7 @@ static void rxrpc_free_preparse_s(struct key_preparsed_payload *);
 static void rxrpc_destroy(struct key *);
 static void rxrpc_destroy_s(struct key *);
 static void rxrpc_describe(const struct key *, struct seq_file *);
-static long rxrpc_read(const struct key *, char __user *, size_t);
+static long rxrpc_read(const struct key *, char *, size_t);
 
 /*
  * rxrpc defined keys take an arbitrary string as the description and an
@@ -1042,12 +1042,12 @@ EXPORT_SYMBOL(rxrpc_get_null_key);
  * - this returns the result in XDR form
  */
 static long rxrpc_read(const struct key *key,
-		       char __user *buffer, size_t buflen)
+		       char *buffer, size_t buflen)
 {
 	const struct rxrpc_key_token *token;
 	const struct krb5_principal *princ;
 	size_t size;
-	__be32 __user *xdr, *oldxdr;
+	__be32 *xdr, *oldxdr;
 	u32 cnlen, toksize, ntoks, tok, zero;
 	u16 toksizes[AFSTOKEN_MAX];
 	int loop;
@@ -1124,30 +1124,25 @@ static long rxrpc_read(const struct key *key,
 	if (!buffer || buflen < size)
 		return size;
 
-	xdr = (__be32 __user *) buffer;
+	xdr = (__be32 *)buffer;
 	zero = 0;
 #define ENCODE(x)				\
 	do {					\
-		__be32 y = htonl(x);		\
-		if (put_user(y, xdr++) < 0)	\
-			goto fault;		\
+		*xdr++ = htonl(x);		\
 	} while(0)
 #define ENCODE_DATA(l, s)						\
 	do {								\
 		u32 _l = (l);						\
 		ENCODE(l);						\
-		if (copy_to_user(xdr, (s), _l) != 0)			\
-			goto fault;					\
-		if (_l & 3 &&						\
-		    copy_to_user((u8 __user *)xdr + _l, &zero, 4 - (_l & 3)) != 0) \
-			goto fault;					\
+		memcpy(xdr, (s), _l);					\
+		if (_l & 3)						\
+			memcpy((u8 *)xdr + _l, &zero, 4 - (_l & 3));	\
 		xdr += (_l + 3) >> 2;					\
 	} while(0)
 #define ENCODE64(x)					\
 	do {						\
 		__be64 y = cpu_to_be64(x);		\
-		if (copy_to_user(xdr, &y, 8) != 0)	\
-			goto fault;			\
+		memcpy(xdr, &y, 8);			\
 		xdr += 8 >> 2;				\
 	} while(0)
 #define ENCODE_STR(s)				\
@@ -1238,8 +1233,4 @@ static long rxrpc_read(const struct key *key,
 	ASSERTCMP((char __user *) xdr - buffer, ==, size);
 	_leave(" = %zu", size);
 	return size;
-
-fault:
-	_leave(" = -EFAULT");
-	return -EFAULT;
 }
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index 001abe530a0d..82008f900930 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -352,7 +352,7 @@ void big_key_describe(const struct key *key, struct seq_file *m)
  * read the key data
  * - the key's semaphore is read-locked
  */
-long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
+long big_key_read(const struct key *key, char *buffer, size_t buflen)
 {
 	size_t datalen = (size_t)key->payload.data[big_key_len];
 	long ret;
@@ -391,9 +391,8 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 
 		ret = datalen;
 
-		/* copy decrypted data to user */
-		if (copy_to_user(buffer, buf->virt, datalen) != 0)
-			ret = -EFAULT;
+		/* copy out decrypted data */
+		memcpy(buffer, buf->virt, datalen);
 
 err_fput:
 		fput(file);
@@ -401,9 +400,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 		big_key_free_buffer(buf);
 	} else {
 		ret = datalen;
-		if (copy_to_user(buffer, key->payload.data[big_key_data],
-				 datalen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, key->payload.data[big_key_data], datalen);
 	}
 
 	return ret;
diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 60720f58cbe0..f6797ba44bf7 100644
--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -902,14 +902,14 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
 }
 
 /*
- * encrypted_read - format and copy the encrypted data to userspace
+ * encrypted_read - format and copy out the encrypted data
  *
  * The resulting datablob format is:
  * <master-key name> <decrypted data length> <encrypted iv> <encrypted data>
  *
  * On success, return to userspace the encrypted key datablob size.
  */
-static long encrypted_read(const struct key *key, char __user *buffer,
+static long encrypted_read(const struct key *key, char *buffer,
 			   size_t buflen)
 {
 	struct encrypted_key_payload *epayload;
@@ -957,8 +957,7 @@ static long encrypted_read(const struct key *key, char __user *buffer,
 	key_put(mkey);
 	memzero_explicit(derived_key, sizeof(derived_key));
 
-	if (copy_to_user(buffer, ascii_buf, asciiblob_len) != 0)
-		ret = -EFAULT;
+	memcpy(buffer, ascii_buf, asciiblob_len);
 	kzfree(ascii_buf);
 
 	return asciiblob_len;
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 9b898c969558..81f68e434b9f 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -797,6 +797,21 @@ long keyctl_keyring_search(key_serial_t ringid,
 	return ret;
 }
 
+/*
+ * Call the read method
+ */
+static long __keyctl_read_key(struct key *key, char *buffer, size_t buflen)
+{
+	long ret;
+
+	down_read(&key->sem);
+	ret = key_validate(key);
+	if (ret == 0)
+		ret = key->type->read(key, buffer, buflen);
+	up_read(&key->sem);
+	return ret;
+}
+
 /*
  * Read a key's payload.
  *
@@ -844,16 +859,42 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 
 	/* the key is probably readable - now try to read it */
 can_read_key:
-	ret = -EOPNOTSUPP;
-	if (key->type->read) {
-		/* Read the data with the semaphore held (since we might sleep)
+	if (!key->type->read) {
+		ret = -EOPNOTSUPP;
+		goto error2;
+	}
+
+	if (!buffer || !buflen) {
+		/* Get the key length from the read method */
+		ret = __keyctl_read_key(key, NULL, 0);
+	} else {
+
+		/*
+		 * Read the data with the semaphore held (since we might sleep)
 		 * to protect against the key being updated or revoked.
+		 *
+		 * Allocating a temporary buffer to hold the keys before
+		 * transferring them to user buffer to avoid potential
+		 * deadlock involving page fault and mmap_sem.
+		 */
+		char *tmpbuf = kmalloc(buflen, GFP_KERNEL);
+
+		if (!tmpbuf) {
+			ret = -ENOMEM;
+			goto error2;
+		}
+		ret = __keyctl_read_key(key, tmpbuf, buflen);
+
+		/*
+		 * Read methods will just return the required length
+		 * without any copying if the provided length isn't big
+		 * enough.
 		 */
-		down_read(&key->sem);
-		ret = key_validate(key);
-		if (ret == 0)
-			ret = key->type->read(key, buffer, buflen);
-		up_read(&key->sem);
+		if ((ret > 0) && (ret <= buflen)) {
+			if (copy_to_user(buffer, tmpbuf, ret))
+				ret = -EFAULT;
+		}
+		kzfree(tmpbuf);
 	}
 
 error2:
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index febf36c6ddc5..5ca620d31cd3 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -459,7 +459,6 @@ static int keyring_read_iterator(const void *object, void *data)
 {
 	struct keyring_read_iterator_context *ctx = data;
 	const struct key *key = keyring_ptr_to_key(object);
-	int ret;
 
 	kenter("{%s,%d},,{%zu/%zu}",
 	       key->type->name, key->serial, ctx->count, ctx->buflen);
@@ -467,10 +466,7 @@ static int keyring_read_iterator(const void *object, void *data)
 	if (ctx->count >= ctx->buflen)
 		return 1;
 
-	ret = put_user(key->serial, ctx->buffer);
-	if (ret < 0)
-		return ret;
-	ctx->buffer++;
+	*ctx->buffer++ = key->serial;
 	ctx->count += sizeof(key->serial);
 	return 0;
 }
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index ecba39c93fd9..41e9735006d0 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -22,7 +22,7 @@ static int request_key_auth_instantiate(struct key *,
 static void request_key_auth_describe(const struct key *, struct seq_file *);
 static void request_key_auth_revoke(struct key *);
 static void request_key_auth_destroy(struct key *);
-static long request_key_auth_read(const struct key *, char __user *, size_t);
+static long request_key_auth_read(const struct key *, char *, size_t);
 
 /*
  * The request-key authorisation key type definition.
@@ -80,7 +80,7 @@ static void request_key_auth_describe(const struct key *key,
  * - the key's semaphore is read-locked
  */
 static long request_key_auth_read(const struct key *key,
-				  char __user *buffer, size_t buflen)
+				  char *buffer, size_t buflen)
 {
 	struct request_key_auth *rka = dereference_key_locked(key);
 	size_t datalen;
@@ -97,8 +97,7 @@ static long request_key_auth_read(const struct key *key,
 		if (buflen > datalen)
 			buflen = datalen;
 
-		if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, rka->callout_info, buflen);
 	}
 
 	return ret;
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index d2c5ec1e040b..8001ab07e63b 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -1130,11 +1130,10 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
  * trusted_read - copy the sealed blob data to userspace in hex.
  * On success, return to userspace the trusted key datablob size.
  */
-static long trusted_read(const struct key *key, char __user *buffer,
+static long trusted_read(const struct key *key, char *buffer,
 			 size_t buflen)
 {
 	const struct trusted_key_payload *p;
-	char *ascii_buf;
 	char *bufp;
 	int i;
 
@@ -1143,18 +1142,9 @@ static long trusted_read(const struct key *key, char __user *buffer,
 		return -EINVAL;
 
 	if (buffer && buflen >= 2 * p->blob_len) {
-		ascii_buf = kmalloc_array(2, p->blob_len, GFP_KERNEL);
-		if (!ascii_buf)
-			return -ENOMEM;
-
-		bufp = ascii_buf;
+		bufp = buffer;
 		for (i = 0; i < p->blob_len; i++)
 			bufp = hex_byte_pack(bufp, p->blob[i]);
-		if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) {
-			kzfree(ascii_buf);
-			return -EFAULT;
-		}
-		kzfree(ascii_buf);
 	}
 	return 2 * p->blob_len;
 }
diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 6f12de4ce549..07d4287e9084 100644
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -168,7 +168,7 @@ EXPORT_SYMBOL_GPL(user_describe);
  * read the key data
  * - the key's semaphore is read-locked
  */
-long user_read(const struct key *key, char __user *buffer, size_t buflen)
+long user_read(const struct key *key, char *buffer, size_t buflen)
 {
 	const struct user_key_payload *upayload;
 	long ret;
@@ -181,8 +181,7 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen)
 		if (buflen > upayload->datalen)
 			buflen = upayload->datalen;
 
-		if (copy_to_user(buffer, upayload->data, buflen) != 0)
-			ret = -EFAULT;
+		memcpy(buffer, upayload->data, buflen);
 	}
 
 	return ret;
-- 
2.18.1

[PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

By allocating a kernel buffer with a user-supplied buffer length, it
is possible that a false positive ENOMEM error may be returned because
the user-supplied length is just too large even if the system do have
enough memory to hold the actual key data.

Moreover, if the buffer length is larger than the maximum amount of
memory that can be returned by kmalloc() (2^(MAX_ORDER-1) number of
pages), a warning message will also be printed.

To reduce this possibility, we set a threshold (page size) over which we
do check the actual key length first before allocating a buffer of the
right size to hold it. The threshold is arbitrary, it is just used to
trigger a buffer length check. It does not limit the actual key length
as long as there is enough memory to satisfy the memory request.

To further avoid large buffer allocation failure due to page
fragmentation, kvmalloc() is used to allocate the buffer so that vmapped
pages can be used when there is not a large enough contiguous set of
pages available for allocation.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 security/keys/internal.h | 12 ++++++++++++
 security/keys/keyctl.c   | 41 ++++++++++++++++++++++++++++++++--------
 2 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/security/keys/internal.h b/security/keys/internal.h
index ba3e2da14cef..6d0ca48ae9a5 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -16,6 +16,8 @@
 #include <linux/keyctl.h>
 #include <linux/refcount.h>
 #include <linux/compat.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
 
 struct iovec;
 
@@ -349,4 +351,14 @@ static inline void key_check(const struct key *key)
 
 #endif
 
+/*
+ * Helper function to clear and free a kvmalloc'ed memory object.
+ */
+static inline void __kvzfree(const void *addr, size_t len)
+{
+	if (addr) {
+		memset((void *)addr, 0, len);
+		kvfree(addr);
+	}
+}
 #endif /* _INTERNAL_H */
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 81f68e434b9f..07eaa46d344c 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -339,7 +339,7 @@ long keyctl_update_key(key_serial_t id,
 	payload = NULL;
 	if (plen) {
 		ret = -ENOMEM;
-		payload = kmalloc(plen, GFP_KERNEL);
+		payload = kvmalloc(plen, GFP_KERNEL);
 		if (!payload)
 			goto error;
 
@@ -360,7 +360,7 @@ long keyctl_update_key(key_serial_t id,
 
 	key_ref_put(key_ref);
 error2:
-	kzfree(payload);
+	__kvzfree(payload, plen);
 error:
 	return ret;
 }
@@ -877,13 +877,24 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 		 * transferring them to user buffer to avoid potential
 		 * deadlock involving page fault and mmap_sem.
 		 */
-		char *tmpbuf = kmalloc(buflen, GFP_KERNEL);
+		char *tmpbuf = NULL;
+		size_t tmpbuflen = buflen;
 
-		if (!tmpbuf) {
-			ret = -ENOMEM;
-			goto error2;
+		/*
+		 * To prevent memory allocation failure with an arbitrary
+		 * large user-supplied buflen, we do a key length check
+		 * before allocating a buffer of the right size to hold
+		 * key data if it exceeds a threshold (PAGE_SIZE).
+		 */
+		if (buflen <= PAGE_SIZE) {
+allocbuf:
+			tmpbuf = kvmalloc(tmpbuflen, GFP_KERNEL);
+			if (!tmpbuf) {
+				ret = -ENOMEM;
+				goto error2;
+			}
 		}
-		ret = __keyctl_read_key(key, tmpbuf, buflen);
+		ret = __keyctl_read_key(key, tmpbuf, tmpbuflen);
 
 		/*
 		 * Read methods will just return the required length
@@ -891,10 +902,24 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 		 * enough.
 		 */
 		if ((ret > 0) && (ret <= buflen)) {
+			/*
+			 * It is possible, though unlikely, that the key
+			 * changes in between the up_read->down_read period.
+			 * If the key becomes longer, we will have to
+			 * allocate a larger buffer and redo the key read
+			 * again.
+			 */
+			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
+				if (unlikely(tmpbuf))
+					__kvzfree(tmpbuf, tmpbuflen);
+				tmpbuflen = ret;
+				goto allocbuf;
+			}
+
 			if (copy_to_user(buffer, tmpbuf, ret))
 				ret = -EFAULT;
 		}
-		kzfree(tmpbuf);
+		__kvzfree(tmpbuf, tmpbuflen);
 	}
 
 error2:
-- 
2.18.1

[PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

By allocating a kernel buffer with a user-supplied buffer length, it
is possible that a false positive ENOMEM error may be returned because
the user-supplied length is just too large even if the system do have
enough memory to hold the actual key data.

Moreover, if the buffer length is larger than the maximum amount of
memory that can be returned by kmalloc() (2^(MAX_ORDER-1) number of
pages), a warning message will also be printed.

To reduce this possibility, we set a threshold (page size) over which we
do check the actual key length first before allocating a buffer of the
right size to hold it. The threshold is arbitrary, it is just used to
trigger a buffer length check. It does not limit the actual key length
as long as there is enough memory to satisfy the memory request.

To further avoid large buffer allocation failure due to page
fragmentation, kvmalloc() is used to allocate the buffer so that vmapped
pages can be used when there is not a large enough contiguous set of
pages available for allocation.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 security/keys/internal.h | 12 ++++++++++++
 security/keys/keyctl.c   | 41 ++++++++++++++++++++++++++++++++--------
 2 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/security/keys/internal.h b/security/keys/internal.h
index ba3e2da14cef..6d0ca48ae9a5 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -16,6 +16,8 @@
 #include <linux/keyctl.h>
 #include <linux/refcount.h>
 #include <linux/compat.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
 
 struct iovec;
 
@@ -349,4 +351,14 @@ static inline void key_check(const struct key *key)
 
 #endif
 
+/*
+ * Helper function to clear and free a kvmalloc'ed memory object.
+ */
+static inline void __kvzfree(const void *addr, size_t len)
+{
+	if (addr) {
+		memset((void *)addr, 0, len);
+		kvfree(addr);
+	}
+}
 #endif /* _INTERNAL_H */
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 81f68e434b9f..07eaa46d344c 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -339,7 +339,7 @@ long keyctl_update_key(key_serial_t id,
 	payload = NULL;
 	if (plen) {
 		ret = -ENOMEM;
-		payload = kmalloc(plen, GFP_KERNEL);
+		payload = kvmalloc(plen, GFP_KERNEL);
 		if (!payload)
 			goto error;
 
@@ -360,7 +360,7 @@ long keyctl_update_key(key_serial_t id,
 
 	key_ref_put(key_ref);
 error2:
-	kzfree(payload);
+	__kvzfree(payload, plen);
 error:
 	return ret;
 }
@@ -877,13 +877,24 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 		 * transferring them to user buffer to avoid potential
 		 * deadlock involving page fault and mmap_sem.
 		 */
-		char *tmpbuf = kmalloc(buflen, GFP_KERNEL);
+		char *tmpbuf = NULL;
+		size_t tmpbuflen = buflen;
 
-		if (!tmpbuf) {
-			ret = -ENOMEM;
-			goto error2;
+		/*
+		 * To prevent memory allocation failure with an arbitrary
+		 * large user-supplied buflen, we do a key length check
+		 * before allocating a buffer of the right size to hold
+		 * key data if it exceeds a threshold (PAGE_SIZE).
+		 */
+		if (buflen <= PAGE_SIZE) {
+allocbuf:
+			tmpbuf = kvmalloc(tmpbuflen, GFP_KERNEL);
+			if (!tmpbuf) {
+				ret = -ENOMEM;
+				goto error2;
+			}
 		}
-		ret = __keyctl_read_key(key, tmpbuf, buflen);
+		ret = __keyctl_read_key(key, tmpbuf, tmpbuflen);
 
 		/*
 		 * Read methods will just return the required length
@@ -891,10 +902,24 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 		 * enough.
 		 */
 		if ((ret > 0) && (ret <= buflen)) {
+			/*
+			 * It is possible, though unlikely, that the key
+			 * changes in between the up_read->down_read period.
+			 * If the key becomes longer, we will have to
+			 * allocate a larger buffer and redo the key read
+			 * again.
+			 */
+			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
+				if (unlikely(tmpbuf))
+					__kvzfree(tmpbuf, tmpbuflen);
+				tmpbuflen = ret;
+				goto allocbuf;
+			}
+
 			if (copy_to_user(buffer, tmpbuf, ret))
 				ret = -EFAULT;
 		}
-		kzfree(tmpbuf);
+		__kvzfree(tmpbuf, tmpbuflen);
 	}
 
 error2:
-- 
2.18.1

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> +			 * It is possible, though unlikely, that the key
> +			 * changes in between the up_read->down_read period.
> +			 * If the key becomes longer, we will have to
> +			 * allocate a larger buffer and redo the key read
> +			 * again.
> +			 */
> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {

Shouldn't you check that tmpbuflen stays below buflen (why else
you had made copy of buflen otherwise)?

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> +			 * It is possible, though unlikely, that the key
> +			 * changes in between the up_read->down_read period.
> +			 * If the key becomes longer, we will have to
> +			 * allocate a larger buffer and redo the key read
> +			 * again.
> +			 */
> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {

Shouldn't you check that tmpbuflen stays below buflen (why else
you had made copy of buflen otherwise)?

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>> +			 * It is possible, though unlikely, that the key
>> +			 * changes in between the up_read->down_read period.
>> +			 * If the key becomes longer, we will have to
>> +			 * allocate a larger buffer and redo the key read
>> +			 * again.
>> +			 */
>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> Shouldn't you check that tmpbuflen stays below buflen (why else
> you had made copy of buflen otherwise)?

The check above this thunk:

if ((ret > 0) && (ret <= buflen)) {

will make sure that ret will not be larger than buflen. So tmpbuflen
will never be bigger than buflen.

Cheers,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>> +			 * It is possible, though unlikely, that the key
>> +			 * changes in between the up_read->down_read period.
>> +			 * If the key becomes longer, we will have to
>> +			 * allocate a larger buffer and redo the key read
>> +			 * again.
>> +			 */
>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> Shouldn't you check that tmpbuflen stays below buflen (why else
> you had made copy of buflen otherwise)?

The check above this thunk:

if ((ret > 0) && (ret <= buflen)) {

will make sure that ret will not be larger than buflen. So tmpbuflen
will never be bigger than buflen.

Cheers,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> > On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> >> +			 * It is possible, though unlikely, that the key
> >> +			 * changes in between the up_read->down_read period.
> >> +			 * If the key becomes longer, we will have to
> >> +			 * allocate a larger buffer and redo the key read
> >> +			 * again.
> >> +			 */
> >> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> > Shouldn't you check that tmpbuflen stays below buflen (why else
> > you had made copy of buflen otherwise)?
> 
> The check above this thunk:
> 
> if ((ret > 0) && (ret <= buflen)) {
> 
> will make sure that ret will not be larger than buflen. So tmpbuflen
> will never be bigger than buflen.

Ah right, of course, thanks.

What would go wrong if the condition was instead
((ret > 0) && (ret <= tmpbuflen))?

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> > On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> >> +			 * It is possible, though unlikely, that the key
> >> +			 * changes in between the up_read->down_read period.
> >> +			 * If the key becomes longer, we will have to
> >> +			 * allocate a larger buffer and redo the key read
> >> +			 * again.
> >> +			 */
> >> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> > Shouldn't you check that tmpbuflen stays below buflen (why else
> > you had made copy of buflen otherwise)?
> 
> The check above this thunk:
> 
> if ((ret > 0) && (ret <= buflen)) {
> 
> will make sure that ret will not be larger than buflen. So tmpbuflen
> will never be bigger than buflen.

Ah right, of course, thanks.

What would go wrong if the condition was instead
((ret > 0) && (ret <= tmpbuflen))?

/Jarkko

Re: [PATCH v5 1/2] KEYS: Don't write out to userspace while holding key semaphore

[David Howells]

Waiman Long <longman@redhat.com> wrote:

> +		if ((ret > 0) && (ret <= buflen)) {

That's a bit excessive on the bracketage, btw, but don't worry about it unless
you respin the patches.

David

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>>>> +			 * It is possible, though unlikely, that the key
>>>> +			 * changes in between the up_read->down_read period.
>>>> +			 * If the key becomes longer, we will have to
>>>> +			 * allocate a larger buffer and redo the key read
>>>> +			 * again.
>>>> +			 */
>>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
>>> Shouldn't you check that tmpbuflen stays below buflen (why else
>>> you had made copy of buflen otherwise)?
>> The check above this thunk:
>>
>> if ((ret > 0) && (ret <= buflen)) {
>>
>> will make sure that ret will not be larger than buflen. So tmpbuflen
>> will never be bigger than buflen.
> Ah right, of course, thanks.
>
> What would go wrong if the condition was instead
> ((ret > 0) && (ret <= tmpbuflen))?

That if statement is a check to see if the actual key length is longer
than the user-supplied buffer (buflen). If that is the case, it will
just return the expected length without storing anything into the user
buffer. For the case that buflen >= ret > tmpbuflen, the revised check
above will incorrectly skip the storing step causing the caller to
incorrectly think the key is there in the buffer.

Maybe I should clarify that a bit more in the comment.

Cheers,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>>>> +			 * It is possible, though unlikely, that the key
>>>> +			 * changes in between the up_read->down_read period.
>>>> +			 * If the key becomes longer, we will have to
>>>> +			 * allocate a larger buffer and redo the key read
>>>> +			 * again.
>>>> +			 */
>>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
>>> Shouldn't you check that tmpbuflen stays below buflen (why else
>>> you had made copy of buflen otherwise)?
>> The check above this thunk:
>>
>> if ((ret > 0) && (ret <= buflen)) {
>>
>> will make sure that ret will not be larger than buflen. So tmpbuflen
>> will never be bigger than buflen.
> Ah right, of course, thanks.
>
> What would go wrong if the condition was instead
> ((ret > 0) && (ret <= tmpbuflen))?

That if statement is a check to see if the actual key length is longer
than the user-supplied buffer (buflen). If that is the case, it will
just return the expected length without storing anything into the user
buffer. For the case that buflen >= ret > tmpbuflen, the revised check
above will incorrectly skip the storing step causing the caller to
incorrectly think the key is there in the buffer.

Maybe I should clarify that a bit more in the comment.

Cheers,
Longman

Re: [PATCH v5 1/2] KEYS: Don't write out to userspace while holding key semaphore

[Waiman Long]

On 3/20/20 4:20 AM, David Howells wrote:
> Waiman Long <longman@redhat.com> wrote:
>
>> +		if ((ret > 0) && (ret <= buflen)) {
> That's a bit excessive on the bracketage, btw, but don't worry about it unless
> you respin the patches.

Got it.

Thanks,
Longman

Re: [PATCH v5 1/2] KEYS: Don't write out to userspace while holding key semaphore

[Waiman Long]

On 3/20/20 4:20 AM, David Howells wrote:
> Waiman Long <longman@redhat.com> wrote:
>
>> +		if ((ret > 0) && (ret <= buflen)) {
> That's a bit excessive on the bracketage, btw, but don't worry about it unless
> you respin the patches.

Got it.

Thanks,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote:
> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
> > On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
> >> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> >>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> >>>> +			 * It is possible, though unlikely, that the key
> >>>> +			 * changes in between the up_read->down_read period.
> >>>> +			 * If the key becomes longer, we will have to
> >>>> +			 * allocate a larger buffer and redo the key read
> >>>> +			 * again.
> >>>> +			 */
> >>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> >>> Shouldn't you check that tmpbuflen stays below buflen (why else
> >>> you had made copy of buflen otherwise)?
> >> The check above this thunk:
> >>
> >> if ((ret > 0) && (ret <= buflen)) {
> >>
> >> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen.  > > Ah right, of course, thanks.
> >
> > What would go wrong if the condition was instead
> > ((ret > 0) && (ret <= tmpbuflen))?
> 
> That if statement is a check to see if the actual key length is longer
> than the user-supplied buffer (buflen). If that is the case, it will
> just return the expected length without storing anything into the user
> buffer. For the case that buflen >= ret > tmpbuflen, the revised check
> above will incorrectly skip the storing step causing the caller to
> incorrectly think the key is there in the buffer.
> 
> Maybe I should clarify that a bit more in the comment.

OK, right because it is possible in-between tmpbuflen could be
larger. Got it.

I think that longish key_data and key_data_len would be better
names than tmpbuf and tpmbuflen.

Also the comments are somewat overkill IMHO.

I'd replace them along the lines of

/* Cap the user supplied buffer length to PAGE_SIZE. */

/* Key data can change as we don not hold key->sem. */

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote:
> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
> > On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
> >> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> >>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> >>>> +			 * It is possible, though unlikely, that the key
> >>>> +			 * changes in between the up_read->down_read period.
> >>>> +			 * If the key becomes longer, we will have to
> >>>> +			 * allocate a larger buffer and redo the key read
> >>>> +			 * again.
> >>>> +			 */
> >>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> >>> Shouldn't you check that tmpbuflen stays below buflen (why else
> >>> you had made copy of buflen otherwise)?
> >> The check above this thunk:
> >>
> >> if ((ret > 0) && (ret <= buflen)) {
> >>
> >> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen.  > > Ah right, of course, thanks.
> >
> > What would go wrong if the condition was instead
> > ((ret > 0) && (ret <= tmpbuflen))?
> 
> That if statement is a check to see if the actual key length is longer
> than the user-supplied buffer (buflen). If that is the case, it will
> just return the expected length without storing anything into the user
> buffer. For the case that buflen >= ret > tmpbuflen, the revised check
> above will incorrectly skip the storing step causing the caller to
> incorrectly think the key is there in the buffer.
> 
> Maybe I should clarify that a bit more in the comment.

OK, right because it is possible in-between tmpbuflen could be
larger. Got it.

I think that longish key_data and key_data_len would be better
names than tmpbuf and tpmbuflen.

Also the comments are somewat overkill IMHO.

I'd replace them along the lines of

/* Cap the user supplied buffer length to PAGE_SIZE. */

/* Key data can change as we don not hold key->sem. */

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/20/20 10:35 AM, Jarkko Sakkinen wrote:
> On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote:
>> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
>>> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
>>>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
>>>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>>>>>> +			 * It is possible, though unlikely, that the key
>>>>>> +			 * changes in between the up_read->down_read period.
>>>>>> +			 * If the key becomes longer, we will have to
>>>>>> +			 * allocate a larger buffer and redo the key read
>>>>>> +			 * again.
>>>>>> +			 */
>>>>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
>>>>> Shouldn't you check that tmpbuflen stays below buflen (why else
>>>>> you had made copy of buflen otherwise)?
>>>> The check above this thunk:
>>>>
>>>> if ((ret > 0) && (ret <= buflen)) {
>>>>
>>>> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen.  > > Ah right, of course, thanks.
>>> What would go wrong if the condition was instead
>>> ((ret > 0) && (ret <= tmpbuflen))?
>> That if statement is a check to see if the actual key length is longer
>> than the user-supplied buffer (buflen). If that is the case, it will
>> just return the expected length without storing anything into the user
>> buffer. For the case that buflen >= ret > tmpbuflen, the revised check
>> above will incorrectly skip the storing step causing the caller to
>> incorrectly think the key is there in the buffer.
>>
>> Maybe I should clarify that a bit more in the comment.
> OK, right because it is possible in-between tmpbuflen could be
> larger. Got it.
>
> I think that longish key_data and key_data_len would be better
> names than tmpbuf and tpmbuflen.
>
> Also the comments are somewat overkill IMHO.
>
> I'd replace them along the lines of
>
> /* Cap the user supplied buffer length to PAGE_SIZE. */
>
> /* Key data can change as we don not hold key->sem. */

I am fine with the rename, will sent out a v6 soon.

Cheers,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Waiman Long]

On 3/20/20 10:35 AM, Jarkko Sakkinen wrote:
> On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote:
>> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote:
>>> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
>>>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
>>>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
>>>>>> +			 * It is possible, though unlikely, that the key
>>>>>> +			 * changes in between the up_read->down_read period.
>>>>>> +			 * If the key becomes longer, we will have to
>>>>>> +			 * allocate a larger buffer and redo the key read
>>>>>> +			 * again.
>>>>>> +			 */
>>>>>> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
>>>>> Shouldn't you check that tmpbuflen stays below buflen (why else
>>>>> you had made copy of buflen otherwise)?
>>>> The check above this thunk:
>>>>
>>>> if ((ret > 0) && (ret <= buflen)) {
>>>>
>>>> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen.  > > Ah right, of course, thanks.
>>> What would go wrong if the condition was instead
>>> ((ret > 0) && (ret <= tmpbuflen))?
>> That if statement is a check to see if the actual key length is longer
>> than the user-supplied buffer (buflen). If that is the case, it will
>> just return the expected length without storing anything into the user
>> buffer. For the case that buflen >= ret > tmpbuflen, the revised check
>> above will incorrectly skip the storing step causing the caller to
>> incorrectly think the key is there in the buffer.
>>
>> Maybe I should clarify that a bit more in the comment.
> OK, right because it is possible in-between tmpbuflen could be
> larger. Got it.
>
> I think that longish key_data and key_data_len would be better
> names than tmpbuf and tpmbuflen.
>
> Also the comments are somewat overkill IMHO.
>
> I'd replace them along the lines of
>
> /* Cap the user supplied buffer length to PAGE_SIZE. */
>
> /* Key data can change as we don not hold key->sem. */

I am fine with the rename, will sent out a v6 soon.

Cheers,
Longman

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[David Howells]

Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:

> /* Key data can change as we don not hold key->sem. */

I think you mean "we don't".

David

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Fri, Mar 20, 2020 at 11:55:10PM +0000, David Howells wrote:
> Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> 
> > /* Key data can change as we don not hold key->sem. */
> 
> I think you mean "we don't".

Oops, typo. Yes, thanks.

/Jarkko

Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

[Jarkko Sakkinen]

On Fri, Mar 20, 2020 at 11:55:10PM +0000, David Howells wrote:
> Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
> 
> > /* Key data can change as we don not hold key->sem. */
> 
> I think you mean "we don't".

Oops, typo. Yes, thanks.

/Jarkko