linux-kernel - [PATCH 4.9 072/153] ext4: fix use-after-iput when fscrypt contexts are inconsistent

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Date:   Fri, 10 Mar 2017 10:08:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        Theodore Tso <tytso@....edu>
Subject: [PATCH 4.9 072/153] ext4: fix use-after-iput when fscrypt contexts are inconsistent

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@...gle.com>

commit dd01b690f8f4b1e414f89e5a9a5326bf720d6652 upstream.

In the case where the child's encryption context was inconsistent with
its parent directory, we were using inode->i_sb and inode->i_ino after
the inode had already been iput().  Fix this by doing the iput() in the
correct places.

Note: only ext4 had this bug, not f2fs and ubifs.

Fixes: d9cdc9033181 ("ext4 crypto: enforce context consistency")
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/namei.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1616,13 +1616,15 @@ static struct dentry *ext4_lookup(struct
 		    !fscrypt_has_permitted_context(dir, inode)) {
 			int nokey = ext4_encrypted_inode(inode) &&
 				!fscrypt_has_encryption_key(inode);
-			iput(inode);
-			if (nokey)
+			if (nokey) {
+				iput(inode);
 				return ERR_PTR(-ENOKEY);
+			}
 			ext4_warning(inode->i_sb,
 				     "Inconsistent encryption contexts: %lu/%lu",
 				     (unsigned long) dir->i_ino,
 				     (unsigned long) inode->i_ino);
+			iput(inode);
 			return ERR_PTR(-EPERM);
 		}
 	}