[PATCH] jfs: validate max amount of blocks before allocation.

[Aleksei Filippov <halip0503@gmail.com>]

From: Alexei Filippov <halip0503@gmail.com>

The lack of checking bmp->db_max_freebud in extBalloc() can lead to
shift out of bounds, so this patch prevents undefined behavior,
because bmp->db_max_freebud == -1 only if there
is no free space.

Signed-off-by: Aleksei Filippov <halip0503@gmail.com>
Reported-and-tested-by: syzbot+5f088f29593e6b4c8db8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=01abadbd6ae6a08b1f1987aa61554c6b3ac19ff2
---
 fs/jfs/jfs_extent.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/jfs/jfs_extent.c b/fs/jfs/jfs_extent.c
index ae99a7e232ee..a82751e6c47f 100644
--- a/fs/jfs/jfs_extent.c
+++ b/fs/jfs/jfs_extent.c
@@ -311,6 +311,11 @@ extBalloc(struct inode *ip, s64 hint, s64 * nblocks, s64 * blkno)
 	 * blocks in the map. in that case, we'll start off with the
 	 * maximum free.
 	 */
+
+	/* give up if no space left */
+	if (bmp->db_maxfreebud == -1)
+		return -ENOSPC;
+
 	max = (s64) 1 << bmp->db_maxfreebud;
 	if (*nblocks >= max && *nblocks > nbperpage)
 		nb = nblks = (max > nbperpage) ? max : nbperpage;
-- 
2.25.1