[PATCH AUTOSEL 5.8 117/132] gfs2: add validation checks for size of superblock

Sasha Levin
2020-10-26T23:58:57Z

From: Anant Thazhemadam <anant.thazhemadam@gmail.com>

[ Upstream commit 0ddc5154b24c96f20e94d653b0a814438de6032b ]

In gfs2_check_sb(), no validation checks are performed with regards to
the size of the superblock.
syzkaller detected a slab-out-of-bounds bug that was primarily caused
because the block size for a superblock was set to zero.
A valid size for a superblock is a power of 2 between 512 and PAGE_SIZE.
Performing validation checks and ensuring that the size of the superblock
is valid fixes this bug.

Reported-by: syzbot+af90d47a37376844e731@syzkaller.appspotmail.com
Tested-by: syzbot+af90d47a37376844e731@syzkaller.appspotmail.com
Suggested-by: Andrew Price <anprice@redhat.com>
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
[Minor code reordering.]
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/gfs2/ops_fstype.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 5bd602a290f72..03c33fc03c055 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -169,15 +169,19 @@ static int gfs2_check_sb(struct gfs2_sbd *sdp, int silent)
return -EINVAL;
}

- /* If format numbers match exactly, we're done. */
-
- if (sb->sb_fs_format == GFS2_FORMAT_FS &&
- sb->sb_multihost_format == GFS2_FORMAT_MULTI)
- return 0;
+ if (sb->sb_fs_format != GFS2_FORMAT_FS ||
+ sb->sb_multihost_format != GFS2_FORMAT_MULTI) {
+ fs_warn(sdp, "Unknown on-disk format, unable to mount\n");
+ return -EINVAL;
+ }

- fs_warn(sdp, "Unknown on-disk format, unable to mount\n");
+ if (sb->sb_bsize < 512 || sb->sb_bsize > PAGE_SIZE ||
+ (sb->sb_bsize & (sb->sb_bsize - 1))) {
+ pr_warn("Invalid superblock size\n");
+ return -EINVAL;
+ }

- return -EINVAL;
+ return 0;
}

static void end_bio_io_page(struct bio *bio)
--
2.25.1