BACKPORT: ext4: fail ext4_iget for root directory if unallocated
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
Backport Note: As EFSCORRUPTED does not exist in 3.8, use EIO
BUG=chromium:839356
TEST=None
Change-Id: Iaa2cf501cc246b23c6ba84e3dd6ad46323d581f7
Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
(cherry picked from commit 8e4b5eae5decd9dfe5a4ee369c22028f90ab4c44)
Signed-off-by: Zubin Mithra <zsm@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1042607
Reviewed-by: Guenter Roeck <groeck@chromium.org>
(cherry picked from commit bf83884c035532941682c96b340b9cd060d2fab8)
Reviewed-on: https://chromium-review.googlesource.com/1055115
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 22c5c67..4f1cf14 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3880,6 +3880,12 @@
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 = -EIO;
+ 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 >