linux-kernel - Re: UBSAN: shift-out-of-bounds in exfat_fill

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 25 Jan 2021 18:39:18 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     syzbot <syzbot+da4fe66aaadd3c2e2d1c@...kaller.appspotmail.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        namjae.jeon@...sung.com, sj1557.seo@...sung.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: UBSAN: shift-out-of-bounds in exfat_fill_super

On Mon, Jan 25, 2021 at 09:33:14AM -0800, syzbot wrote:
> UBSAN: shift-out-of-bounds in fs/exfat/super.c:471:28
> shift exponent 4294967294 is too large for 32-bit type 'int'

This is an integer underflow:

        sbi->dentries_per_clu = 1 <<
                (sbi->cluster_size_bits - DENTRY_SIZE_BITS);

I think the problem is that there is no validation of sect_per_clus_bits.
We should check it is at least DENTRY_SIZE_BITS and probably that it's
less than ... 16?  64?  I don't know what legitimate values are in this
field, but I would imagine that 255 is completely unacceptable.