linux-kernel - Re: [PATCH][linux-next] net/smc: prevent NULL dereference in smc_find_rdma_v2_device

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Date:   Tue, 19 Oct 2021 08:33:51 +0200
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Tim Gardner <tim.gardner@...onical.com>, linux-s390@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][linux-next] net/smc: prevent NULL dereference in
 smc_find_rdma_v2_device_serv()

On 18/10/2021 20:31, Tim Gardner wrote:
> Coverity complains of a possible NULL dereference in smc_find_rdma_v2_device_serv().
> 
> 1782        smc_v2_ext = smc_get_clc_v2_ext(pclc);
> CID 121151 (#1 of 1): Dereference null return value (NULL_RETURNS)
> 5. dereference: Dereferencing a pointer that might be NULL smc_v2_ext when calling smc_clc_match_eid. [show details]
> 1783        if (!smc_clc_match_eid(ini->negotiated_eid, smc_v2_ext, NULL, NULL))
> 1784                goto not_found;
> 
> Fix this by checking for NULL.

Hmm that's a fundamental question for me: do we want to make the code checkers happy?
While I understand that those warnings give an uneasy feeling I am not sure
if the code should have additional (unneeded) checks only to avoid them.

In this case all NULL checks are initially done in smc_listen_v2_check(), 
afterwards no more NULL checks are needed. When we would like to add them
then a lot more checks are needed, e.g. 3 times in smc_find_ism_v2_device_serv()
(not sure why coverity does not complain about them, too).

Thoughts?