jfs: validate max amount of blocks before allocation.

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>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+5f088f29593e6b4c8db8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=01abadbd6ae6a08b1f1987aa61554c6b3ac19ff2

diff --git a/fs/jfs/jfs_extent.c b/fs/jfs/jfs_extent.c
index adaa9ad50d4c8e38e1299296c398f176a9c5471d..63d21822d309be4f06acbb52af28b9cdfef4d173 100644 (file)
--- 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;