[PATCH] jfs : fix shift-out-of-bounds in dbUpdatePMap

[Manas Ghandat]

Currently there is no bound check for number of logical blocks per
page (bmp->db_l2nbperpage). Added the required bound check for the
calculation of dmap.

Reported-by: syzbot+91ad2b52815a08caf4ea@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=91ad2b52815a08caf4ea
Fixes: 4d81715fc5df ("[PATCH] fs/jfs: Conversion to generic boolean")
Signed-off-by: Manas Ghandat <ghandatmanas@xxxxxxxxx>
---
 fs/jfs/jfs_dmap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index a3eb1e826947..6a5df296fdc8 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -467,6 +467,10 @@ dbUpdatePMap(struct inode *ipbmap,
 	lastlblkno = 0;
 	for (rem = nblocks; rem > 0; rem -= nblks, blkno += nblks) {
 		/* get the buffer for the current dmap. */
+
+		if (bmp->db_l2nbperpage > L2BPERDMAP)
+			return -EIO;
+
 		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
 		if (lblkno != lastlblkno) {
 			if (mp) {
-- 
2.37.2