[PATCH v3 0/2] Fix crash in trace_rpcgss_context due to 0-length acceptor

[PATCH v3 0/2] Fix crash in trace_rpcgss_context due to 0-length acceptor

[Dave Wysochanski]

Changes from v2
* Move simple_get_bytes and simple_get_netobj into private header

This small patchset fixes a kernel crash when the rpcgss_context trace event is
enabled and IO is in flight when a kerberos ticket expires.  The crash occurs
because the acceptor name may be 0 bytes long and the gss_fill_context() function
does not handle it properly.  This causes the ctx->gc_acceptor.data to be
ZERO_SIZE_PTR which is not properly recognized by the tracepoint code.

The first patch is a simple refactor and eliminates duplicate helper functions
related to the crash.  The second patch is the actual fix inside one of the
helper functions due to the definition of an opaque XDR object.  This object
is defined in RFC 4506 (see section 4.10), where 'length' is an integer in a
range including 0.

Reproducer

# Enable the tracepoint and mount the share
trace-cmd start -e rpcgss:*
mount -osec=krb5 nfs-server:/export /mnt/nfs

# Obtain a kerberos ticket
# Set ticket lifetime to something small like 20 seconds
su test -c "kinit -l 20 test"

# Sleep for a portion of the ticket lifetime so we are writing while the ticket expires
sleep 10

# Now run some IO long enough that the ticket expires midway
dd if=/dev/urandom of=/mnt/nfs/file bs=1M count=100


Dave Wysochanski (2):
  SUNRPC: Move simple_get_bytes and simple_get_netobj into private
    header
  SUNRPC: Handle 0 length opaque XDR object data properly

 include/linux/sunrpc/xdr.h              |  3 +--
 net/sunrpc/auth_gss/auth_gss.c          | 30 +---------------------
 net/sunrpc/auth_gss/auth_gss_internal.h | 45 +++++++++++++++++++++++++++++++++
 net/sunrpc/auth_gss/gss_krb5_mech.c     | 31 ++---------------------
 4 files changed, 49 insertions(+), 60 deletions(-)
 create mode 100644 net/sunrpc/auth_gss/auth_gss_internal.h

-- 
1.8.3.1

[PATCH v3 1/2] SUNRPC: Move simple_get_bytes and simple_get_netobj into private header

[Dave Wysochanski]

Remove duplicated helper functions to parse opaque XDR objects
and place inside new file net/sunrpc/auth_gss/auth_gss_internal.h.
In the new file carry the license and copyright from the source file
net/sunrpc/auth_gss/auth_gss.c.  Finally, update the comment inside
include/linux/sunrpc/xdr.h since lockd is not the only user of
struct xdr_netobj.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
---
 include/linux/sunrpc/xdr.h              |  3 +--
 net/sunrpc/auth_gss/auth_gss.c          | 30 +----------------------
 net/sunrpc/auth_gss/auth_gss_internal.h | 42 +++++++++++++++++++++++++++++++++
 net/sunrpc/auth_gss/gss_krb5_mech.c     | 31 ++----------------------
 4 files changed, 46 insertions(+), 60 deletions(-)
 create mode 100644 net/sunrpc/auth_gss/auth_gss_internal.h

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 19b6dea27367..b26213ae8c1a 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -25,8 +25,7 @@
 #define XDR_QUADLEN(l)		(((l) + 3) >> 2)
 
 /*
- * Generic opaque `network object.' At the kernel level, this type
- * is used only by lockd.
+ * Generic opaque `network object.'
  */
 #define XDR_MAX_NETOBJ		1024
 struct xdr_netobj {
diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 4ecc2a959567..5f42aa5fc612 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -29,6 +29,7 @@
 #include <linux/uaccess.h>
 #include <linux/hashtable.h>
 
+#include "auth_gss_internal.h"
 #include "../netns.h"
 
 #include <trace/events/rpcgss.h>
@@ -125,35 +126,6 @@ struct gss_auth {
 	clear_bit(RPCAUTH_CRED_NEW, &cred->cr_flags);
 }
 
-static const void *
-simple_get_bytes(const void *p, const void *end, void *res, size_t len)
-{
-	const void *q = (const void *)((const char *)p + len);
-	if (unlikely(q > end || q < p))
-		return ERR_PTR(-EFAULT);
-	memcpy(res, p, len);
-	return q;
-}
-
-static inline const void *
-simple_get_netobj(const void *p, const void *end, struct xdr_netobj *dest)
-{
-	const void *q;
-	unsigned int len;
-
-	p = simple_get_bytes(p, end, &len, sizeof(len));
-	if (IS_ERR(p))
-		return p;
-	q = (const void *)((const char *)p + len);
-	if (unlikely(q > end || q < p))
-		return ERR_PTR(-EFAULT);
-	dest->data = kmemdup(p, len, GFP_NOFS);
-	if (unlikely(dest->data == NULL))
-		return ERR_PTR(-ENOMEM);
-	dest->len = len;
-	return q;
-}
-
 static struct gss_cl_ctx *
 gss_cred_get_ctx(struct rpc_cred *cred)
 {
diff --git a/net/sunrpc/auth_gss/auth_gss_internal.h b/net/sunrpc/auth_gss/auth_gss_internal.h
new file mode 100644
index 000000000000..c5603242b54b
--- /dev/null
+++ b/net/sunrpc/auth_gss/auth_gss_internal.h
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * linux/net/sunrpc/auth_gss/auth_gss_internal.h
+ *
+ * Internal definitions for RPCSEC_GSS client authentication
+ *
+ * Copyright (c) 2000 The Regents of the University of Michigan.
+ * All rights reserved.
+ *
+ */
+#include <linux/err.h>
+#include <linux/string.h>
+#include <linux/sunrpc/xdr.h>
+
+static inline const void *
+simple_get_bytes(const void *p, const void *end, void *res, size_t len)
+{
+	const void *q = (const void *)((const char *)p + len);
+	if (unlikely(q > end || q < p))
+		return ERR_PTR(-EFAULT);
+	memcpy(res, p, len);
+	return q;
+}
+
+static inline const void *
+simple_get_netobj(const void *p, const void *end, struct xdr_netobj *dest)
+{
+	const void *q;
+	unsigned int len;
+
+	p = simple_get_bytes(p, end, &len, sizeof(len));
+	if (IS_ERR(p))
+		return p;
+	q = (const void *)((const char *)p + len);
+	if (unlikely(q > end || q < p))
+		return ERR_PTR(-EFAULT);
+	dest->data = kmemdup(p, len, GFP_NOFS);
+	if (unlikely(dest->data == NULL))
+		return ERR_PTR(-ENOMEM);
+	dest->len = len;
+	return q;
+}
diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c b/net/sunrpc/auth_gss/gss_krb5_mech.c
index ae9acf3a7389..1c092b05c2bb 100644
--- a/net/sunrpc/auth_gss/gss_krb5_mech.c
+++ b/net/sunrpc/auth_gss/gss_krb5_mech.c
@@ -21,6 +21,8 @@
 #include <linux/sunrpc/xdr.h>
 #include <linux/sunrpc/gss_krb5_enctypes.h>
 
+#include "auth_gss_internal.h"
+
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 # define RPCDBG_FACILITY	RPCDBG_AUTH
 #endif
@@ -143,35 +145,6 @@
 	return NULL;
 }
 
-static const void *
-simple_get_bytes(const void *p, const void *end, void *res, int len)
-{
-	const void *q = (const void *)((const char *)p + len);
-	if (unlikely(q > end || q < p))
-		return ERR_PTR(-EFAULT);
-	memcpy(res, p, len);
-	return q;
-}
-
-static const void *
-simple_get_netobj(const void *p, const void *end, struct xdr_netobj *res)
-{
-	const void *q;
-	unsigned int len;
-
-	p = simple_get_bytes(p, end, &len, sizeof(len));
-	if (IS_ERR(p))
-		return p;
-	q = (const void *)((const char *)p + len);
-	if (unlikely(q > end || q < p))
-		return ERR_PTR(-EFAULT);
-	res->data = kmemdup(p, len, GFP_NOFS);
-	if (unlikely(res->data == NULL))
-		return ERR_PTR(-ENOMEM);
-	res->len = len;
-	return q;
-}
-
 static inline const void *
 get_key(const void *p, const void *end,
 	struct krb5_ctx *ctx, struct crypto_sync_skcipher **res)
-- 
1.8.3.1

[PATCH v3 2/2] SUNRPC: Handle 0 length opaque XDR object data properly

[Dave Wysochanski]

When handling an auth_gss downcall, it's possible to get 0-length
opaque object for the acceptor.  In the case of a 0-length XDR
object, make sure simple_get_netobj() fills in dest->data = NULL,
and does not continue to kmemdup() which will set
dest->data = ZERO_SIZE_PTR for the acceptor.

The trace event code can handle NULL but not ZERO_SIZE_PTR for a
string, and so without this patch the rpcgss_context trace event
will crash the kernel as follows:

[  162.887992] BUG: kernel NULL pointer dereference, address: 0000000000000010
[  162.898693] #PF: supervisor read access in kernel mode
[  162.900830] #PF: error_code(0x0000) - not-present page
[  162.902940] PGD 0 P4D 0
[  162.904027] Oops: 0000 [#1] SMP PTI
[  162.905493] CPU: 4 PID: 4321 Comm: rpc.gssd Kdump: loaded Not tainted 5.10.0 #133
[  162.908548] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[  162.910978] RIP: 0010:strlen+0x0/0x20
[  162.912505] Code: 48 89 f9 74 09 48 83 c1 01 80 39 00 75 f7 31 d2 44 0f b6 04 16 44 88 04 11 48 83 c2 01 45 84 c0 75 ee c3 0f 1f 80 00 00 00 00 <80> 3f 00 74 10 48 89 f8 48 83 c0 01 80 38 00 75 f7 48 29 f8 c3 31
[  162.920101] RSP: 0018:ffffaec900c77d90 EFLAGS: 00010202
[  162.922263] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000fffde697
[  162.925158] RDX: 000000000000002f RSI: 0000000000000080 RDI: 0000000000000010
[  162.928073] RBP: 0000000000000010 R08: 0000000000000e10 R09: 0000000000000000
[  162.930976] R10: ffff8e698a590cb8 R11: 0000000000000001 R12: 0000000000000e10
[  162.933883] R13: 00000000fffde697 R14: 000000010034d517 R15: 0000000000070028
[  162.936777] FS:  00007f1e1eb93700(0000) GS:ffff8e6ab7d00000(0000) knlGS:0000000000000000
[  162.940067] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  162.942417] CR2: 0000000000000010 CR3: 0000000104eba000 CR4: 00000000000406e0
[  162.945300] Call Trace:
[  162.946428]  trace_event_raw_event_rpcgss_context+0x84/0x140 [auth_rpcgss]
[  162.949308]  ? __kmalloc_track_caller+0x35/0x5a0
[  162.951224]  ? gss_pipe_downcall+0x3a3/0x6a0 [auth_rpcgss]
[  162.953484]  gss_pipe_downcall+0x585/0x6a0 [auth_rpcgss]
[  162.955953]  rpc_pipe_write+0x58/0x70 [sunrpc]
[  162.957849]  vfs_write+0xcb/0x2c0
[  162.959264]  ksys_write+0x68/0xe0
[  162.960706]  do_syscall_64+0x33/0x40
[  162.962238]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  162.964346] RIP: 0033:0x7f1e1f1e57df

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
---
 net/sunrpc/auth_gss/auth_gss_internal.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/auth_gss/auth_gss_internal.h b/net/sunrpc/auth_gss/auth_gss_internal.h
index c5603242b54b..f6d9631bd9d0 100644
--- a/net/sunrpc/auth_gss/auth_gss_internal.h
+++ b/net/sunrpc/auth_gss/auth_gss_internal.h
@@ -34,9 +34,12 @@
 	q = (const void *)((const char *)p + len);
 	if (unlikely(q > end || q < p))
 		return ERR_PTR(-EFAULT);
-	dest->data = kmemdup(p, len, GFP_NOFS);
-	if (unlikely(dest->data == NULL))
-		return ERR_PTR(-ENOMEM);
+	if (len) {
+		dest->data = kmemdup(p, len, GFP_NOFS);
+		if (unlikely(dest->data == NULL))
+			return ERR_PTR(-ENOMEM);
+	} else
+		dest->data = NULL;
 	dest->len = len;
 	return q;
 }
-- 
1.8.3.1