On 6/5/23 9:01AM, Siddh Raman Pant wrote:

In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block number inside dbFree(). db_l2nbperpage, which is the log2 number of blocks per page, is passed as an argument to BLKTODMAP which uses it for shifting.

Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is too big. This happens because the large value is set without any validation in dbMount() at line 181.

Thus, make sure that db_l2nbperpage is correct while mounting.

Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d22571... Cc: stable@vger.kernel.org Signed-off-by: Siddh Raman Pant code@siddh.me

---

fs/jfs/jfs_dmap.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c index a3eb1e826947..62f058822a3a 100644 --- a/fs/jfs/jfs_dmap.c +++ b/fs/jfs/jfs_dmap.c @@ -178,7 +178,13 @@ int dbMount(struct inode *ipbmap) dbmp_le = (struct dbmap_disk *) mp->data; bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize); bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);

• bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
• if (bmp->db_l2nbperpage > L2MAXL0SIZE) {

Actually the sanity check should be much smaller. The maximum value should be L2PSIZE - log2(MINBLOCKSIZE). In reality, I think it's always zero.

Shaggy

• err = -EINVAL;
  

• goto err_release_metapage;
  

• }
• bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag); if (!bmp->db_numag) { err = -EINVAL;