From: "Namjae Jeon" <namjae.jeon@samsung.com>
To: "'Matthew Wilcox'" <willy@infradead.org>
Cc: <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<sj1557.seo@samsung.com>, <syzkaller-bugs@googlegroups.com>,
"'syzbot'"
<syzbot+da4fe66aaadd3c2e2d1c@syzkaller.appspotmail.com>
Subject: RE: UBSAN: shift-out-of-bounds in exfat_fill_super
Date: Tue, 26 Jan 2021 13:40:08 +0900 [thread overview]
Message-ID: <051e01d6f39d$537a0910$fa6e1b30$@samsung.com> (raw)
In-Reply-To: <20210125183918.GH308988@casper.infradead.org>
> 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.
exfat specification describe sect_per_clus_bits field of boot sector could be at most 32 and
at least 0. And sect_size_bits can also affect this calculation, It also needs validation.
I will fix it.
Thanks!
next prev parent reply other threads:[~2021-01-26 22:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 17:33 UBSAN: shift-out-of-bounds in exfat_fill_super syzbot
2021-01-25 18:39 ` Matthew Wilcox
2021-01-26 4:33 ` Randy Dunlap
2021-01-26 5:14 ` Namjae Jeon
2021-01-26 4:40 ` Namjae Jeon [this message]
2021-01-26 5:08 ` Namjae Jeon
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