jfs: Fix shift-out-of-bounds in dbDiscardAG

commit 7063b80268e2593e58bee8a8d709c2f3ff93e2f2 upstream.

When searching for the next smaller log2 block, BLKSTOL2() returned 0,
causing shift exponent -1 to be negative.

This patch fixes the issue by exiting the loop directly when negative
shift is found.

Reported-by: syzbot+61be3359d2ee3467e7e4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61be3359d2ee3467e7e4
Signed-off-by: Pei Li <peili.dev@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Zhi Yang <Zhi.Yang@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 8f4c55c711ba06aa91d24ef2731c687901518462..9dccebbee55ad093ae07c5c471592e30a5b24cec 100644 (file)
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1698,6 +1698,8 @@ s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
                } else if (rc == -ENOSPC) {
                        /* search for next smaller log2 block */
                        l2nb = BLKSTOL2(nblocks) - 1;
+                       if (unlikely(l2nb < 0))
+                               break;
                        nblocks = 1LL << l2nb;
                } else {
                        /* Trim any already allocated blocks */