jfs: fix divide error in dbNextAG

Syzbot reported divide error in dbNextAG(). The problem was in missing
validation check for malicious image.

Syzbot crafted an image with bmp->db_numag equal to 0. There wasn't any
validation checks, but dbNextAG() blindly use bmp->db_numag in divide
expression

Fix it by validating bmp->db_numag in dbMount() and return an error if
image is malicious

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+46f5c25af73eb8330eb6@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 91f4ec9..d8502f4 100644 (file)
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -148,6 +148,7 @@ static const s8 budtab[256] = {
  *     0       - success
  *     -ENOMEM - insufficient memory
  *     -EIO    - i/o error
+ *     -EINVAL - wrong bmap data
  */
 int dbMount(struct inode *ipbmap)
 {
@@ -179,6 +180,12 @@ 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);
        bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
+       if (!bmp->db_numag) {
+               release_metapage(mp);
+               kfree(bmp);
+               return -EINVAL;
+       }
+
        bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
        bmp->db_maxag = le32_to_cpu(dbmp_le->dn_maxag);
        bmp->db_agpref = le32_to_cpu(dbmp_le->dn_agpref);