linux-kernel - Re: [PATCH 0/2] Prevent potential write out of bounds

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Message-ID: <00d4a104c17d92562f03042c31ea664b@overdrivepizza.com>
Date:   Thu, 31 Aug 2023 22:46:49 -0700
From:   Joao Moreira <joao@...rdrivepizza.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     pablo@...filter.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kadlec@...filter.org, fw@...len.de,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        rkannoth@...vell.com, wojciech.drewek@...el.com,
        steen.hegenlund@...rohip.com, keescook@...omium.org,
        Joao Moreira <joao.moreira@...el.com>
Subject: Re: [PATCH 0/2] Prevent potential write out of bounds

On 2023-08-31 18:28, Jakub Kicinski wrote:
> On Thu, 31 Aug 2023 18:04:35 -0700 joao@...rdrivepizza.com wrote:
>> The function flow_rule_alloc in net/core/flow_offload.c [2] gets an
>> unsigned int num_actions (line 10) and later traverses the actions in
>> the rule (line 24) setting hw.stats to FLOW_ACTION_HW_STATS_DONT_CARE.
>> 
>> Within the same file, the loop in the line 24 compares a signed int
>> (i) to an unsigned int (num_actions), and then uses i as an array
>> index. If an integer overflow happens, then the array within the loop
>> is wrongly indexed, causing a write out of bounds.
>> 
>> After checking with maintainers, it seems that the front-end caps the
>> maximum value of num_action, thus it is not possible to reach the 
>> given
>> write out of bounds, yet, still, to prevent disasters it is better to
>> fix the signedness here.
> 
> How did you find this? The commit messages should include info
> about how the issue was discovered.

Sure, I'll wait a bit longer for more suggestions and add the info in a 
next patch version.

Meanwhile, fwiiw, I stumbled on the bug when I was reading Nick 
Gregory's write-up on CVE-2022-25636 [1], which happens nearby but is 
not exactly this issue.

Tks,
Joao

[1] - https://nickgregory.me/post/2022/03/12/cve-2022-25636/