From 670f8ce56dd0632dc29a0322e188cc73ce3c6b92 Mon Sep 17 00:00:00 2001
From: Andrew Price <anprice@redhat.com>
Date: Wed, 17 Aug 2022 13:22:00 +0100
Subject: [PATCH] gfs2: Check sb_bsize_shift after reading superblock
Git-commit: 670f8ce56dd0632dc29a0322e188cc73ce3c6b92
Patch-mainline: v6.1-rc1
References: git-fixes
Fuzzers like to scribble over sb_bsize_shift but in reality it's very
unlikely that this field would be corrupted on its own. Nevertheless it
should be checked to avoid the possibility of messy mount errors due to
bad calculations. It's always a fixed value based on the block size so
we can just check that it's the expected value.
Tested with:
mkfs.gfs2 -O -p lock_nolock /dev/vdb
for i in 0 -1 64 65 32 33; do
gfs2_edit -p sb field sb_bsize_shift $i /dev/vdb
mount /dev/vdb /mnt/test && umount /mnt/test
done
Before this patch we get a withdraw after
[ 76.413681] gfs2: fsid=loop0.0: fatal: invalid metadata block
[ 76.413681] bh = 19 (type: exp=5, found=4)
[ 76.413681] function = gfs2_meta_buffer, file = fs/gfs2/meta_io.c, line = 492
and with UBSAN configured we also get complaints like
[ 76.373395] UBSAN: shift-out-of-bounds in fs/gfs2/ops_fstype.c:295:19
[ 76.373815] shift exponent 4294967287 is too large for 64-bit type 'long unsigned int'
After the patch, these complaints don't appear, mount fails immediately
and we get an explanation in dmesg.
Reported-by: syzbot+dcf33a7aae997956fe06@syzkaller.appspotmail.com
Signed-off-by: Andrew Price <anprice@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>
---
fs/gfs2/ops_fstype.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -172,7 +172,10 @@ static int gfs2_check_sb(struct gfs2_sbd
pr_warn("Invalid superblock size\n");
return -EINVAL;
}
-
+ if (sb->sb_bsize_shift != ffs(sb->sb_bsize) - 1) {
+ pr_warn("Invalid block size shift\n");
+ return -EINVAL;
+ }
return 0;
}