This is a note to let you know that I've just added the patch titled
fscrypt: clean up and improve dentry revalidation
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fscrypt-clean-up-and-improve-dentry-revalidation.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From foo@baz Sun Nov 1 11:35:18 AM CET 2020
From: Eric Biggers <[email protected]>
Date: Sat, 31 Oct 2020 15:05:49 -0700
Subject: fscrypt: clean up and improve dentry revalidation
To: [email protected]
Cc: [email protected], [email protected],
[email protected], [email protected], Theodore
Ts'o <[email protected]>
Message-ID: <[email protected]>
From: Eric Biggers <[email protected]>
commit 6cc248684d3d23bbd073ae2fa73d3416c0558909 upstream.
Make various improvements to fscrypt dentry revalidation:
- Don't try to handle the case where the per-directory key is removed,
as this can't happen without the inode (and dentries) being evicted.
- Flag ciphertext dentries rather than plaintext dentries, since it's
ciphertext dentries that need the special handling.
- Avoid doing unnecessary work for non-ciphertext dentries.
- When revalidating ciphertext dentries, try to set up the directory's
i_crypt_info to make sure the key is really still absent, rather than
invalidating all negative dentries as the previous code did. An old
comment suggested we can't do this for locking reasons, but AFAICT
this comment was outdated and it actually works fine.
Signed-off-by: Eric Biggers <[email protected]>
Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/crypto/crypto.c | 58 ++++++++++++++++++++++++------------------------
fs/crypto/hooks.c | 4 +--
include/linux/dcache.h | 2 -
include/linux/fscrypt.h | 6 +---
4 files changed, 35 insertions(+), 35 deletions(-)
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -314,45 +314,47 @@ int fscrypt_decrypt_page(const struct in
EXPORT_SYMBOL(fscrypt_decrypt_page);
/*
- * Validate dentries for encrypted directories to make sure we aren't
- * potentially caching stale data after a key has been added or
- * removed.
+ * Validate dentries in encrypted directories to make sure we aren't
potentially
+ * caching stale dentries after a key has been added.
*/
static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
{
struct dentry *dir;
- int dir_has_key, cached_with_key;
+ int err;
+ int valid;
+
+ /*
+ * Plaintext names are always valid, since fscrypt doesn't support
+ * reverting to ciphertext names without evicting the directory's inode
+ * -- which implies eviction of the dentries in the directory.
+ */
+ if (!(dentry->d_flags & DCACHE_ENCRYPTED_NAME))
+ return 1;
+
+ /*
+ * Ciphertext name; valid if the directory's key is still unavailable.
+ *
+ * Although fscrypt forbids rename() on ciphertext names, we still must
+ * use dget_parent() here rather than use ->d_parent directly. That's
+ * because a corrupted fs image may contain directory hard links, which
+ * the VFS handles by moving the directory's dentry tree in the dcache
+ * each time ->lookup() finds the directory and it already has a dentry
+ * elsewhere. Thus ->d_parent can be changing, and we must safely grab
+ * a reference to some ->d_parent to prevent it from being freed.
+ */
if (flags & LOOKUP_RCU)
return -ECHILD;
dir = dget_parent(dentry);
- if (!IS_ENCRYPTED(d_inode(dir))) {
- dput(dir);
- return 0;
- }
-
- spin_lock(&dentry->d_lock);
- cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
- spin_unlock(&dentry->d_lock);
- dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
+ err = fscrypt_get_encryption_info(d_inode(dir));
+ valid = !fscrypt_has_encryption_key(d_inode(dir));
dput(dir);
- /*
- * If the dentry was cached without the key, and it is a
- * negative dentry, it might be a valid name. We can't check
- * if the key has since been made available due to locking
- * reasons, so we fail the validation so ext4_lookup() can do
- * this check.
- *
- * We also fail the validation if the dentry was created with
- * the key present, but we no longer have the key, or vice versa.
- */
- if ((!cached_with_key && d_is_negative(dentry)) ||
- (!cached_with_key && dir_has_key) ||
- (cached_with_key && !dir_has_key))
- return 0;
- return 1;
+ if (err < 0)
+ return err;
+
+ return valid;
}
const struct dentry_operations fscrypt_d_ops = {
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -101,9 +101,9 @@ int __fscrypt_prepare_lookup(struct inod
if (err)
return err;
- if (fscrypt_has_encryption_key(dir)) {
+ if (!fscrypt_has_encryption_key(dir)) {
spin_lock(&dentry->d_lock);
- dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
+ dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
spin_unlock(&dentry->d_lock);
}
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -210,7 +210,7 @@ struct dentry_operations {
#define DCACHE_MAY_FREE 0x00800000
#define DCACHE_FALLTHRU 0x01000000 /* Fall through to
lower layer */
-#define DCACHE_ENCRYPTED_WITH_KEY 0x02000000 /* dir is encrypted with a
valid key */
+#define DCACHE_ENCRYPTED_NAME 0x02000000 /* Encrypted name (dir key
was unavailable) */
#define DCACHE_OP_REAL 0x04000000
#define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with
parent locked shared) */
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -145,10 +145,8 @@ static inline int fscrypt_prepare_rename
* filenames are presented in encrypted form. Therefore, we'll try to set up
* the directory's encryption key, but even without it the lookup can continue.
*
- * To allow invalidating stale dentries if the directory's encryption key is
- * added later, we also install a custom ->d_revalidate() method and use the
- * DCACHE_ENCRYPTED_WITH_KEY flag to indicate whether a given dentry is a
- * plaintext name (flag set) or a ciphertext name (flag cleared).
+ * This also installs a custom ->d_revalidate() method which will invalidate
the
+ * dentry if it was created without the key and the key is later added.
*
* Return: 0 on success, -errno if a problem occurred while setting up the
* encryption key
Patches currently in stable-queue which might be from [email protected] are
queue-4.19/fscrypt-only-set-dentry_operations-on-ciphertext-dentries.patch
queue-4.19/fscrypt-clean-up-and-improve-dentry-revalidation.patch
queue-4.19/fscrypt-fix-race-allowing-rename-and-link-of-ciphertext-dentries.patch
queue-4.19/fs-fscrypt-clear-dcache_encrypted_name-when-unaliasing-directory.patch
queue-4.19/fscrypt-fix-race-where-lookup-marks-plaintext-dentry-as-ciphertext.patch
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