netdev - Re: [PATCH net] s390/qeth: reject oversized SNMP requests

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Date:   Sat, 24 Aug 2019 16:35:06 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jwi@...ux.ibm.com
Cc:     netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        heiko.carstens@...ibm.com, raspl@...ux.ibm.com,
        ubraun@...ux.ibm.com
Subject: Re: [PATCH net] s390/qeth: reject oversized SNMP requests

From: Julian Wiedmann <jwi@...ux.ibm.com>
Date: Fri, 23 Aug 2019 11:29:23 +0200

> Commit d4c08afafa04 ("s390/qeth: streamline SNMP cmd code") removed
> the bounds checking for req_len, under the assumption that the check in
> qeth_alloc_cmd() would suffice.
> 
> But that code path isn't sufficiently robust to handle a user-provided
> data_length, which could overflow (when adding the cmd header overhead)
> before being checked against QETH_BUFSIZE. We end up allocating just a
> tiny iob, and the subsequent copy_from_user() writes past the end of
> that iob.
> 
> Special-case this path and add a coarse bounds check, to protect against
> maliciuous requests. This let's the subsequent code flow do its normal
> job and precise checking, without risk of overflow.
> 
> Fixes: d4c08afafa04 ("s390/qeth: streamline SNMP cmd code")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
> Reviewed-by: Ursula Braun <ubraun@...ux.ibm.com>

Applied.