gfs2: add validation checks for size of superblock

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>

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 5bd602a290f72411a43273a38c484f0e61d602da..03c33fc03c0552d87e3a0ace028e71156fee2d65 100644 (file)
--- 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)