[PATCH 0/5] Add the test_dummy_encryption key on-demand

[PATCH 0/5] Add the test_dummy_encryption key on-demand

[Eric Biggers]

This series eliminates the call to fscrypt_destroy_keyring() from
__put_super(), which is causing confusion because it looks like (but
actually isn't) a sleep-in-atomic bug.  See the thread "block: sleeping
in atomic warnings", i.e.
https://lore.kernel.org/linux-fsdevel/CAHk-=wg6ohuyrmLJYTfEpDbp2Jwnef54gkcpZ3-BYgy4C6UxRQ@mail.gmail.com
and its responses.

To do this, this series makes it so that the key associated with the
"test_dummy_encryption" mount option is added on-demand when files are
accessed, instead of immediately when the filesystem is mounted.

I was going back and forth between this solution and instead having ext4
and f2fs call fscrypt_destroy_keyring() on ->fill_super failure.  (Or
using Linus's suggestion of adding the test dummy key as the very last
step of ->fill_super.)  It does seem ideal to add the key at mount time,
but I ended up going with this solution instead because it reduces the
number of things the individual filesystems have to handle.

Eric Biggers (5):
  fscrypt: add the test dummy encryption key on-demand
  ext4: stop calling fscrypt_add_test_dummy_key()
  f2fs: stop calling fscrypt_add_test_dummy_key()
  fs/super.c: stop calling fscrypt_destroy_keyring() from __put_super()
  fscrypt: clean up fscrypt_add_test_dummy_key()

 fs/crypto/fscrypt_private.h |  4 ++++
 fs/crypto/keyring.c         | 26 +++++++-------------------
 fs/crypto/keysetup.c        | 23 +++++++++++++++++++++--
 fs/crypto/policy.c          |  3 +--
 fs/ext4/super.c             | 13 +------------
 fs/f2fs/super.c             |  6 ------
 fs/super.c                  |  1 -
 include/linux/fscrypt.h     |  9 ---------
 8 files changed, 34 insertions(+), 51 deletions(-)


base-commit: 6d796c50f84ca79f1722bb131799e5a5710c4700
-- 
2.39.1

[PATCH 1/5] fscrypt: add the test dummy encryption key on-demand

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

When the key for an inode is not found but the inode is using the
test_dummy_encryption policy, automatically add the
test_dummy_encryption key to the filesystem keyring.  This eliminates
the need for all the individual filesystems to do this at mount time,
which is a bit tricky to clean up from on failure.

Note: this covers the call to fscrypt_find_master_key() from inode key
setup, but not from the fscrypt ioctls.  So, this isn't *exactly* the
same as the key being present from the very beginning.  I think we can
tolerate that, though, since the inode key setup caller is the only one
that actually matters in the context of test_dummy_encryption.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h |  1 +
 fs/crypto/keysetup.c        | 25 +++++++++++++++++++++++--
 fs/crypto/policy.c          |  3 +--
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 316a778cec0ff..17dd33d9a522e 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -651,6 +651,7 @@ bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
 			    const union fscrypt_policy *policy2);
 int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
 			       struct fscrypt_key_specifier *key_spec);
+const union fscrypt_policy *fscrypt_get_dummy_policy(struct super_block *sb);
 bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
 			      const struct inode *inode);
 int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 94757ccd30568..20323c0ba4c5e 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -438,6 +438,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 				     bool need_dirhash_key,
 				     struct fscrypt_master_key **mk_ret)
 {
+	struct super_block *sb = ci->ci_inode->i_sb;
 	struct fscrypt_key_specifier mk_spec;
 	struct fscrypt_master_key *mk;
 	int err;
@@ -450,8 +451,28 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 	if (err)
 		return err;
 
-	mk = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
-	if (!mk) {
+	mk = fscrypt_find_master_key(sb, &mk_spec);
+	if (unlikely(!mk)) {
+		const union fscrypt_policy *dummy_policy =
+			fscrypt_get_dummy_policy(sb);
+
+		/*
+		 * Add the test_dummy_encryption key on-demand.  In principle,
+		 * it should be added at mount time.  Do it here instead so that
+		 * the individual filesystems don't need to worry about adding
+		 * this key at mount time and cleaning up on mount failure.
+		 */
+		if (dummy_policy &&
+		    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
+			struct fscrypt_dummy_policy tmp = { dummy_policy };
+
+			err = fscrypt_add_test_dummy_key(sb, &tmp);
+			if (err)
+				return err;
+			mk = fscrypt_find_master_key(sb, &mk_spec);
+		}
+	}
+	if (unlikely(!mk)) {
 		if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
 			return -ENOKEY;
 
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 893661b523769..69dca4ff5f488 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -53,8 +53,7 @@ int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
 	}
 }
 
-static const union fscrypt_policy *
-fscrypt_get_dummy_policy(struct super_block *sb)
+const union fscrypt_policy *fscrypt_get_dummy_policy(struct super_block *sb)
 {
 	if (!sb->s_cop->get_dummy_policy)
 		return NULL;
-- 
2.39.1

[PATCH 2/5] ext4: stop calling fscrypt_add_test_dummy_key()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Now that fs/crypto/ adds the test dummy encryption key on-demand when
it's needed, there's no need for individual filesystems to call
fscrypt_add_test_dummy_key().  Remove the call to it from ext4.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/ext4/super.c | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 260c1b3e3ef2c..260bbab25db38 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2635,7 +2635,6 @@ static int ext4_check_test_dummy_encryption(const struct fs_context *fc,
 {
 	const struct ext4_fs_context *ctx = fc->fs_private;
 	const struct ext4_sb_info *sbi = EXT4_SB(sb);
-	int err;
 
 	if (!fscrypt_is_dummy_policy_set(&ctx->dummy_enc_policy))
 		return 0;
@@ -2668,17 +2667,7 @@ static int ext4_check_test_dummy_encryption(const struct fs_context *fc,
 			 "Conflicting test_dummy_encryption options");
 		return -EINVAL;
 	}
-	/*
-	 * fscrypt_add_test_dummy_key() technically changes the super_block, so
-	 * technically it should be delayed until ext4_apply_options() like the
-	 * other changes.  But since we never get here for remounts (see above),
-	 * and this is the last chance to report errors, we do it here.
-	 */
-	err = fscrypt_add_test_dummy_key(sb, &ctx->dummy_enc_policy);
-	if (err)
-		ext4_msg(NULL, KERN_WARNING,
-			 "Error adding test dummy encryption key [%d]", err);
-	return err;
+	return 0;
 }
 
 static void ext4_apply_test_dummy_encryption(struct ext4_fs_context *ctx,
-- 
2.39.1

[PATCH 3/5] f2fs: stop calling fscrypt_add_test_dummy_key()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Now that fs/crypto/ adds the test dummy encryption key on-demand when
it's needed, there's no need for individual filesystems to call
fscrypt_add_test_dummy_key().  Remove the call to it from f2fs.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/f2fs/super.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 1f812b9ce985b..64d3556d61a55 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -540,12 +540,6 @@ static int f2fs_set_test_dummy_encryption(struct super_block *sb,
 				  opt, err);
 		return -EINVAL;
 	}
-	err = fscrypt_add_test_dummy_key(sb, policy);
-	if (err) {
-		f2fs_warn(sbi, "Error adding test dummy encryption key [%d]",
-			  err);
-		return err;
-	}
 	f2fs_warn(sbi, "Test dummy encryption mode enabled");
 	return 0;
 }
-- 
2.39.1

[PATCH 4/5] fs/super.c: stop calling fscrypt_destroy_keyring() from __put_super()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Now that the key associated with the "test_dummy_operation" mount option
is added on-demand when it's needed, rather than immediately when the
filesystem is mounted, fscrypt_destroy_keyring() no longer needs to be
called from __put_super() to avoid a memory leak on mount failure.

Remove this call, which was causing confusion because it appeared to be
a sleep-in-atomic bug (though it wasn't, for a somewhat-subtle reason).

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/super.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index 12c08cb20405d..ce45b7fd27f90 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -291,7 +291,6 @@ static void __put_super(struct super_block *s)
 		WARN_ON(s->s_inode_lru.node);
 		WARN_ON(!list_empty(&s->s_mounts));
 		security_sb_free(s);
-		fscrypt_destroy_keyring(s);
 		put_user_ns(s->s_user_ns);
 		kfree(s->s_subtype);
 		call_rcu(&s->rcu, destroy_super_rcu);
-- 
2.39.1

[PATCH 5/5] fscrypt: clean up fscrypt_add_test_dummy_key()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Now that fscrypt_add_test_dummy_key() is only called by
setup_file_encryption_key() and not by the individual filesystems,
un-export it.  Also change its prototype to take the
fscrypt_key_specifier directly, as the caller already has it.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/fscrypt_private.h |  3 +++
 fs/crypto/keyring.c         | 26 +++++++-------------------
 fs/crypto/keysetup.c        |  4 +---
 include/linux/fscrypt.h     |  9 ---------
 4 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 17dd33d9a522e..0fec2dfc36ebe 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -573,6 +573,9 @@ fscrypt_find_master_key(struct super_block *sb,
 int fscrypt_get_test_dummy_key_identifier(
 			  u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
 
+int fscrypt_add_test_dummy_key(struct super_block *sb,
+			       struct fscrypt_key_specifier *key_spec);
+
 int fscrypt_verify_key_added(struct super_block *sb,
 			     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
 
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 78dd2ff306bd7..78086f8dbda52 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -211,10 +211,6 @@ static int allocate_filesystem_keyring(struct super_block *sb)
  * are still available at this time; this is important because after user file
  * accesses have been allowed, this function may need to evict keys from the
  * keyslots of an inline crypto engine, which requires the block device(s).
- *
- * This is also called when the super_block is being freed.  This is needed to
- * avoid a memory leak if mounting fails after the "test_dummy_encryption"
- * option was processed, as in that case the unmount-time call isn't made.
  */
 void fscrypt_destroy_keyring(struct super_block *sb)
 {
@@ -778,34 +774,26 @@ int fscrypt_get_test_dummy_key_identifier(
 /**
  * fscrypt_add_test_dummy_key() - add the test dummy encryption key
  * @sb: the filesystem instance to add the key to
- * @dummy_policy: the encryption policy for test_dummy_encryption
+ * @key_spec: the key specifier of the test dummy encryption key
  *
- * If needed, add the key for the test_dummy_encryption mount option to the
- * filesystem.  To prevent misuse of this mount option, a per-boot random key is
- * used instead of a hardcoded one.  This makes it so that any encrypted files
- * created using this option won't be accessible after a reboot.
+ * Add the key for the test_dummy_encryption mount option to the filesystem.  To
+ * prevent misuse of this mount option, a per-boot random key is used instead of
+ * a hardcoded one.  This makes it so that any encrypted files created using
+ * this option won't be accessible after a reboot.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_add_test_dummy_key(struct super_block *sb,
-			       const struct fscrypt_dummy_policy *dummy_policy)
+			       struct fscrypt_key_specifier *key_spec)
 {
-	const union fscrypt_policy *policy = dummy_policy->policy;
-	struct fscrypt_key_specifier key_spec;
 	struct fscrypt_master_key_secret secret;
 	int err;
 
-	if (!policy)
-		return 0;
-	err = fscrypt_policy_to_key_spec(policy, &key_spec);
-	if (err)
-		return err;
 	fscrypt_get_test_dummy_secret(&secret);
-	err = add_master_key(sb, &secret, &key_spec);
+	err = add_master_key(sb, &secret, key_spec);
 	wipe_master_key_secret(&secret);
 	return err;
 }
-EXPORT_SYMBOL_GPL(fscrypt_add_test_dummy_key);
 
 /*
  * Verify that the current user has added a master key with the given identifier
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 20323c0ba4c5e..aa94fba9d17e7 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -464,9 +464,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci,
 		 */
 		if (dummy_policy &&
 		    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
-			struct fscrypt_dummy_policy tmp = { dummy_policy };
-
-			err = fscrypt_add_test_dummy_key(sb, &tmp);
+			err = fscrypt_add_test_dummy_key(sb, &mk_spec);
 			if (err)
 				return err;
 			mk = fscrypt_find_master_key(sb, &mk_spec);
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 4f5f8a6512132..44848d870046a 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -309,8 +309,6 @@ fscrypt_free_dummy_policy(struct fscrypt_dummy_policy *dummy_policy)
 /* keyring.c */
 void fscrypt_destroy_keyring(struct super_block *sb);
 int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
-int fscrypt_add_test_dummy_key(struct super_block *sb,
-			       const struct fscrypt_dummy_policy *dummy_policy);
 int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg);
 int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *arg);
 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *arg);
@@ -530,13 +528,6 @@ static inline int fscrypt_ioctl_add_key(struct file *filp, void __user *arg)
 	return -EOPNOTSUPP;
 }
 
-static inline int
-fscrypt_add_test_dummy_key(struct super_block *sb,
-			   const struct fscrypt_dummy_policy *dummy_policy)
-{
-	return 0;
-}
-
 static inline int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg)
 {
 	return -EOPNOTSUPP;
-- 
2.39.1

Re: [PATCH 0/5] Add the test_dummy_encryption key on-demand

[Linus Torvalds]

On Tue, Feb 7, 2023 at 10:21 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> I was going back and forth between this solution and instead having ext4
> and f2fs call fscrypt_destroy_keyring() on ->fill_super failure.  (Or
> using Linus's suggestion of adding the test dummy key as the very last
> step of ->fill_super.)  It does seem ideal to add the key at mount time,
> but I ended up going with this solution instead because it reduces the
> number of things the individual filesystems have to handle.

Well, the diffstat certainly looks nice:

>  8 files changed, 34 insertions(+), 51 deletions(-)

with that

>  fs/super.c                  |  1 -

removing the offending line that made Dan's static detection tool so
unhappy, so this all looks lovely to me.

Thanks,
             Linus

Re: [f2fs-dev] [PATCH 0/5] Add the test_dummy_encryption key on-demand

[patchwork-bot+f2fs]

Hello:

This series was applied to jaegeuk/f2fs.git (dev)
by Eric Biggers <ebiggers@google.com>:

On Tue,  7 Feb 2023 22:21:02 -0800 you wrote:
> This series eliminates the call to fscrypt_destroy_keyring() from
> __put_super(), which is causing confusion because it looks like (but
> actually isn't) a sleep-in-atomic bug.  See the thread "block: sleeping
> in atomic warnings", i.e.
> https://lore.kernel.org/linux-fsdevel/CAHk-=wg6ohuyrmLJYTfEpDbp2Jwnef54gkcpZ3-BYgy4C6UxRQ@mail.gmail.com
> and its responses.
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,1/5] fscrypt: add the test dummy encryption key on-demand
    https://git.kernel.org/jaegeuk/f2fs/c/60e463f0be98
  - [f2fs-dev,2/5] ext4: stop calling fscrypt_add_test_dummy_key()
    https://git.kernel.org/jaegeuk/f2fs/c/7959eb19e4a3
  - [f2fs-dev,3/5] f2fs: stop calling fscrypt_add_test_dummy_key()
    https://git.kernel.org/jaegeuk/f2fs/c/1ad2a626762d
  - [f2fs-dev,4/5] fs/super.c: stop calling fscrypt_destroy_keyring() from __put_super()
    https://git.kernel.org/jaegeuk/f2fs/c/ec64036e6863
  - [f2fs-dev,5/5] fscrypt: clean up fscrypt_add_test_dummy_key()
    https://git.kernel.org/jaegeuk/f2fs/c/097d7c1fcb8d

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html