fscrypt: fix race allowing rename() and link() of ciphertext dentries
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 <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index a9492f7..2e7498a 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -49,7 +49,8 @@
}
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 @@
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 @@
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,
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 09e368a..855f743 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -215,7 +215,8 @@
/* hooks.c */
extern int fscrypt_file_open(struct inode *inode, struct file *filp);
-extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
+extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
+ struct dentry *dentry);
extern int __fscrypt_prepare_rename(struct inode *old_dir,
struct dentry *old_dentry,
struct inode *new_dir,
@@ -401,8 +402,8 @@
return 0;
}
-static inline int __fscrypt_prepare_link(struct inode *inode,
- struct inode *dir)
+static inline int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
+ struct dentry *dentry)
{
return -EOPNOTSUPP;
}
@@ -497,7 +498,7 @@
struct dentry *dentry)
{
if (IS_ENCRYPTED(dir))
- return __fscrypt_prepare_link(d_inode(old_dentry), dir);
+ return __fscrypt_prepare_link(d_inode(old_dentry), dir, dentry);
return 0;
}