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

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Message-ID: <ZPGdihJLKXOj7rDI@calendula>
Date:   Fri, 1 Sep 2023 10:15:06 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     joao@...rdrivepizza.com, 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 Thu, Aug 31, 2023 at 06:28:00PM -0700, 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.

This is net-next material IMO, none of the existing interfaces uses
such a large number of actions for this to be an issue.