From: Eric Biggers <ebiggers@xxxxxxxxxx> commit 159e1de201b6fca10bfec50405a3b53a561096a8 upstream. It's possible to create a duplicate filename in an encrypted directory by creating a file concurrently with adding the encryption key. Specifically, sys_open(O_CREAT) (or sys_mkdir(), sys_mknod(), or sys_symlink()) can lookup the target filename while the directory's encryption key hasn't been added yet, resulting in a negative no-key dentry. The VFS then calls ->create() (or ->mkdir(), ->mknod(), or ->symlink()) because the dentry is negative. Normally, ->create() would return -ENOKEY due to the directory's key being unavailable. However, if the key was added between the dentry lookup and ->create(), then the filesystem will go ahead and try to create the file. If the target filename happens to already exist as a normal name (not a no-key name), a duplicate filename may be added to the directory. In order to fix this, we need to fix the filesystems to prevent ->create(), ->mkdir(), ->mknod(), and ->symlink() on no-key names. (->rename() and ->link() need it too, but those are already handled correctly by fscrypt_prepare_rename() and fscrypt_prepare_link().) In preparation for this, add a helper function fscrypt_is_nokey_name() that filesystems can use to do this check. Use this helper function for the existing checks that fs/crypto/ does for rename and link. Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20201118075609.120337-2-ebiggers@xxxxxxxxxx Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- fs/crypto/hooks.c | 10 +++++----- include/linux/fscrypt.h | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 5 deletions(-) diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c index bb3b7fcfdd48a..a5a40a76b8ed7 100644 --- a/fs/crypto/hooks.c +++ b/fs/crypto/hooks.c @@ -58,8 +58,8 @@ 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) + /* ... in case we looked up no-key name before key was added */ + if (fscrypt_is_nokey_name(dentry)) return -ENOKEY; if (!fscrypt_has_permitted_context(dir, inode)) @@ -83,9 +83,9 @@ 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) + /* ... in case we looked up no-key name(s) before key was added */ + if (fscrypt_is_nokey_name(old_dentry) || + fscrypt_is_nokey_name(new_dentry)) return -ENOKEY; if (old_dir != new_dir) { diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index f622f7460ed8c..032e5bcf97012 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -100,6 +100,35 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry) dentry->d_flags &= ~DCACHE_ENCRYPTED_NAME; } +/** + * fscrypt_is_nokey_name() - test whether a dentry is a no-key name + * @dentry: the dentry to check + * + * This returns true if the dentry is a no-key dentry. A no-key dentry is a + * dentry that was created in an encrypted directory that hasn't had its + * encryption key added yet. Such dentries may be either positive or negative. + * + * When a filesystem is asked to create a new filename in an encrypted directory + * and the new filename's dentry is a no-key dentry, it must fail the operation + * with ENOKEY. This includes ->create(), ->mkdir(), ->mknod(), ->symlink(), + * ->rename(), and ->link(). (However, ->rename() and ->link() are already + * handled by fscrypt_prepare_rename() and fscrypt_prepare_link().) + * + * This is necessary because creating a filename requires the directory's + * encryption key, but just checking for the key on the directory inode during + * the final filesystem operation doesn't guarantee that the key was available + * during the preceding dentry lookup. And the key must have already been + * available during the dentry lookup in order for it to have been checked + * whether the filename already exists in the directory and for the new file's + * dentry not to be invalidated due to it incorrectly having the no-key flag. + * + * Return: %true if the dentry is a no-key name + */ +static inline bool fscrypt_is_nokey_name(const struct dentry *dentry) +{ + return dentry->d_flags & DCACHE_ENCRYPTED_NAME; +} + /* crypto.c */ extern void fscrypt_enqueue_decrypt_work(struct work_struct *); extern struct fscrypt_ctx *fscrypt_get_ctx(gfp_t); @@ -290,6 +319,11 @@ static inline void fscrypt_handle_d_move(struct dentry *dentry) { } +static inline bool fscrypt_is_nokey_name(const struct dentry *dentry) +{ + return false; +} + /* crypto.c */ static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work) { -- 2.29.2
