From mboxrd@z Thu Jan 1 00:00:00 1970 From: Haggai Eran Subject: Re: [PATCH v3 06/17] IB/core: Add support for extended query device caps Date: Wed, 17 Dec 2014 16:12:32 +0200 Message-ID: <54918F50.7020705@mellanox.com> References: <1418310266-9584-1-git-send-email-haggaie@mellanox.com> <1418310266-9584-7-git-send-email-haggaie@mellanox.com> <1418733236.2779.26.camel@opteya.com> <549128B4.5010301@mellanox.com> <1418824811.3334.3.camel@dworkin> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1418824811.3334.3.camel@dworkin> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Yann Droneaud Cc: Roland Dreier , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Liran Liss , Or Gerlitz , Sagi Grimberg , Majd Dibbiny , Jerome Glisse , Eli Cohen List-Id: linux-rdma@vger.kernel.org On 17/12/2014 16:00, Yann Droneaud wrote: > Hi, >=20 > Le mercredi 17 d=C3=A9cembre 2014 =C3=A0 08:54 +0200, Haggai Eran a =C3= =A9crit : >> On 16/12/2014 14:33, Yann Droneaud wrote: >>> Le jeudi 11 d=C3=A9cembre 2014 =C3=A0 17:04 +0200, Haggai Eran a =C3= =A9crit : >>>> static inline int ib_copy_to_udata(struct ib_udata *udata, void *= src, size_t len) >>>> { >>>> - return copy_to_user(udata->outbuf, src, len) ? -EFAULT : 0; >>>> + size_t copy_sz; >>>> + >>>> + copy_sz =3D min_t(size_t, len, udata->outlen); >>>> + return copy_to_user(udata->outbuf, src, copy_sz) ? -EFAULT : 0; >>>> } >>> >>> >>> This is not the place to do this: as I'm guessing the purpose of th= is=20 >>> change from the patch in '[PATCH v3 07/17] IB/core: Add flags for o= n=20 >>> demand paging support', you're trying to handle uverbs call from=20 >>> a userspace program using a previous, shorter ABI. >> >> Yes, that was my intention. >> >>> >>> But that's hidding bug where userspace will get it wrong at passing= the=20 >>> correct buffer / size for all others uverb calls. >>> >>> That cannot work that way. >>> >>> In a previous patchset [1], I've suggested to add a check in=20 >>> ib_copy_{from,to}_udata()[2][3] in order to check the input/output >>> buffer size to not read/write past userspace provided buffer >>> boundaries: in case of mismatch an error would be returned to >>> userspace. >>> >>> With the suggested change here, buffer overflow won't happen, >>> but the error is silently ignored, allowing uverb to return a >>> partial result, which is likely not expected by userspace as >>> it's a bit difficult to handle it gracefully. >>> >>> So this has to be removed, and a check on userspace response >>> buffer must be added to ib_uverbs_ex_query_device() instead. >> >> I agree that we shouldn't silently ignore bugs in userspace, but I'm= not >> sure the alternative is maintainable. If we have in the future N new >> extensions to this verb, will we need to validate the user space giv= en >> output buffer is one of the N possible sizes? >> >=20 > Yes. It would very easy for someone to forget one of the possible sizes, and thus blocking support for an older version of libibverbs. Such a bug would be hard to detect because it requires testing all previous versions of libibverbs. I think the problem you are trying to solve - userspace accidentally setting a smaller response size then required - will be detected immediately when one attempts to use that code. >=20 > Additionnaly the size should be checked related to the flags set in t= he > "comp_mask": eg. requiring IB_USER_VERBS_EX_QUERY_DEVICE_ODP but not > providing the expected response buffer should be an error. In a query verb like EX_QUERY_DEVICE, I would expect the user-space cod= e to request all bits in the comp_mask, since there's very little benefit from requesting a specific set (only a slightly shorter response for th= e system call). The kernel would ignore bits it doesn't know, and the user-space would ignore bits it doesn't know in the response. Regards, Haggai -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html