From: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
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@xxxxxxxxxx>
> Signed-off-by: Julian Wiedmann <jwi@xxxxxxxxxxxxx>
> Reviewed-by: Ursula Braun <ubraun@xxxxxxxxxxxxx>
Applied.
