fs/jfs: Add check for negative db_l2nbperpage

[ Upstream commit 525b861a008143048535011f3816d407940f4bfa ]

l2nbperpage is log2(number of blks per page), and the minimum legal
value should be 0, not negative.

In the case of l2nbperpage being negative, an error will occur
when subsequently used as shift exponent.

Syzbot reported this bug:

UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:799:12
shift exponent -16777216 is negative

Reported-by: syzbot+debee9ab7ae2b34b0307@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=debee9ab7ae2b34b0307
Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index da4f9c3b714fea2b7bfdf24dcc265e78463fd970..a700950429c5fb42fc9d54cb22cefa1e55b3276c 100644 (file)
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -180,7 +180,8 @@ int dbMount(struct inode *ipbmap)
        bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
 
        bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
-       if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE) {
+       if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE ||
+               bmp->db_l2nbperpage < 0) {
                err = -EINVAL;
                goto err_release_metapage;
        }