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From 8e0e94683f8449f4e83b4b563b80eb9c76b9e18f Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Thu, 29 Mar 2018 21:56:09 -0400
Subject: [PATCH] ext4: fail ext4_iget for root directory if unallocated
commit 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44 upstream.
If the root directory has an i_links_count of zero, then when the file
system is mounted, then when ext4_fill_super() notices the problem and
tries to call iput() the root directory in the error return path,
ext4_evict_inode() will try to free the inode on disk, before all of
the file system structures are set up, and this will result in an OOPS
caused by a NULL pointer dereference.
This issue has been assigned CVE-2018-1092.
https://bugzilla.kernel.org/show_bug.cgi?id=199179
https://bugzilla.redhat.com/show_bug.cgi?id=1560777
CVE: CVE-2018-1092
Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=8e0e94683f8449f4e83b4b563b80eb9c76b9e18f]
Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
---
fs/ext4/inode.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 69f017e88e89..09014c3c4207 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4685,6 +4685,12 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
goto bad_inode;
raw_inode = ext4_raw_inode(&iloc);
+ if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
+ EXT4_ERROR_INODE(inode, "root inode unallocated");
+ ret = -EFSCORRUPTED;
+ goto bad_inode;
+ }
+
if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
--
2.20.1
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