linux-kernel - Re: [PATCH] drm/panfrost: Avoid user size passed to kvmalloc()

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] [day] [month] [year] [list]

Message-ID: <68709772-b515-f4ab-676f-2bf1f510dfe6@arm.com>
Date:   Fri, 17 Dec 2021 09:48:13 +0000
From:   Steven Price <steven.price@....com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Rob Herring <robh@...nel.org>, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/panfrost: Avoid user size passed to kvmalloc()

On 17/12/2021 09:28, Dan Carpenter wrote:
> On Fri, Dec 17, 2021 at 09:16:19AM +0000, Steven Price wrote:
>> On 17/12/2021 09:10, Dan Carpenter wrote:
>>> On Fri, Dec 17, 2021 at 08:55:50AM +0000, Steven Price wrote:
>>>> However this one is harder to fix without setting an arbitrary cap on
>>>> the number of BOs during a sumbit. I'm not sure how other drivers handle
>>>> this - the ones I've looked at so far all have the same issue. There's
>>>> obviously the list that Dan already sent, but e.g. msm has the same bug
>>>> in msm_gem_submit.c:submit_create() with an amusing bug where the check
>>>> for (sz > SIZE_MAX) will never hit, although the call is to kzalloc() so
>>>> large allocations are going to fail anyway.
>>>
>>> sz is u64 and SIZE_MAX is ULONG_MAX so the (sz > SIZE_MAX) condition
>>> does work to prevent an integer overflow on 32bit systems.  But it's not
>>> beautiful.
>>
>> sz is the result of struct_size() which returns a size_t, and SIZE_MAX
>> in case of an overflow.
> 
> Correct.
> 
>> However the check is *greater than* SIZE_MAX
>> which will never occur even on 32 bit systems.
> 
> You've missed a part.  We add ((u64)nr_cmds * sizeof(submit->cmd[0]))
> to SIZE_MAX.  If nr_cmds is zero then, whatever, the kzmalloc() will
> fail.  No big deal.  But if it's non-zero then "sz" is larger than
> SIZE_MAX and we allocate a smaller buffer than expected leading to
> memory corruption.

Ah, my bracket matching is obviously off today - somehow I hadn't
noticed that the second line wasn't part of the call to struct_size().

> Btw, it turns out that I had a hand in writing that check so hooray for
> me.  :)  #HoorayForMe

Indeed hooray for you! ;) Although it still all seems like a very
round-a-bout way of enforcing an arbitrary maximum on the size!

Thanks,

Steve