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fscrypt: fix race allowing rename() and link() of ciphertext dentries

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Close some race conditions where fscrypt allowed rename() and link() on
ciphertext dentries that had been looked up just prior to the key being
concurrently added.  It's better to return -ENOKEY in this case.

This avoids doing the nonsensical thing of encrypting the names a second
time when searching for the actual on-disk dir entries.  It also
guarantees that DCACHE_ENCRYPTED_NAME dentries are never rename()d, so
the dcache won't have support all possible combinations of moving
DCACHE_ENCRYPTED_NAME around during __d_move().

Signed-off-by: Eric Biggers <[email protected]>
Signed-off-by: Theodore Ts'o <[email protected]>
This commit is contained in:
Eric Biggers 2019-03-20 11:39:10 -07:00 • committed by Theodore Ts'o
commit 968dd6d0c6
2 changed files with 16 additions and 5 deletions
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12
fs/crypto/hooks.c
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@ -49,7 +49,8 @@ int fscrypt_file_open(struct inode *inode, struct file *filp)
}
EXPORT_SYMBOL_GPL(fscrypt_file_open);
int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
struct dentry *dentry)
{
int err;
@ -57,6 +58,10 @@ int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
if (err)
return err;
/* ... in case we looked up ciphertext name before key was added */
if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
return -ENOKEY;
if (!fscrypt_has_permitted_context(dir, inode))
return -EXDEV;
@ -78,6 +83,11 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
if (err)
return err;
/* ... in case we looked up ciphertext name(s) before key was added */
if ((old_dentry->d_flags | new_dentry->d_flags) &
DCACHE_ENCRYPTED_NAME)
return -ENOKEY;
if (old_dir != new_dir) {
if (IS_ENCRYPTED(new_dir) &&
!fscrypt_has_permitted_context(new_dir,