Re: [PATCH v3 06/17] IB/core: Add support for extended query device caps

[Yann Droneaud <ydroneaud-RlY5vtjFyJ3QT0dZR+AlfA@public.gmane.org>]

Hi,

Le mercredi 17 décembre 2014 à 08:54 +0200, Haggai Eran a écrit :
> On 16/12/2014 14:33, Yann Droneaud wrote:
> > Le jeudi 11 décembre 2014 à 17:04 +0200, Haggai Eran a écrit :
> >>  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 = 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 this 
> > change from the patch in '[PATCH v3 07/17] IB/core: Add flags for on 
> > demand paging support', you're trying to handle uverbs call from 
> > 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 
> > 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 
> > 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 given
> output buffer is one of the N possible sizes?
> 

Yes.

Additionnaly the size should be checked related to the flags set in the
"comp_mask": eg. requiring IB_USER_VERBS_EX_QUERY_DEVICE_ODP but not
providing the expected response buffer should be an error.

Regards.

-- 
Yann Droneaud
OPTEYA


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