[PATCH 4.16 093/196] ext4: fail ext4_iget for root directory if unallocated

From: Greg Kroah-Hartman
Date: Sun Apr 22 2018 - 12:01:16 EST

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


From: Theodore Ts'o <tytso@xxxxxxx>

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.


Reported-by: Wen Xu <wen.xu@xxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/ext4/inode.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4745,6 +4745,12 @@ struct inode *ext4_iget(struct super_blo
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");
+ 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 >