ext4 crypto: use dget_parent() in ext4_d_revalidate()

This avoids potential problems caused by a race where the inode gets
renamed out from its parent directory and the parent directory is
deleted while ext4_d_revalidate() is running.

Fixes: 28b4c263961c
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index 012fd3285147..ea69ce4f6d8f 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -478,13 +478,16 @@ uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
  */
 static int ext4_d_revalidate(struct dentry *dentry, unsigned int flags)
 {
-        struct inode *dir = d_inode(dentry->d_parent);
-        struct ext4_crypt_info *ci = EXT4_I(dir)->i_crypt_info;
+        struct dentry *dir;
+        struct ext4_crypt_info *ci;
         int dir_has_key, cached_with_key;
 
-        if (!ext4_encrypted_inode(dir))
+        dir = dget_parent(dentry);
+        if (!ext4_encrypted_inode(d_inode(dir))) {
+                dput(dir);
                 return 0;
-
+        }
+        ci = EXT4_I(d_inode(dir))->i_crypt_info;
         if (ci && ci->ci_keyring_key &&
             (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
                                           (1 << KEY_FLAG_REVOKED) |
@@ -494,6 +497,7 @@ static int ext4_d_revalidate(struct dentry *dentry, unsigned int flags)
         /* this should eventually be an flag in d_flags */
         cached_with_key = dentry->d_fsdata != NULL;
         dir_has_key = (ci != NULL);
+        dput(dir);
 
         /*
          * If the dentry was cached without the key, and it is a