----- On Jul 2, 2018, at 4:52 PM, Linus Torvalds torvalds@xxxxxxxxxxxxxxxxxxxx wrote:
> On Mon, Jul 2, 2018 at 1:41 PM Mathieu Desnoyers
> <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>>
>> - if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
>> + if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)) ||
>> + rseq_cs->abort_ip >= TASK_SIZE)
>> return -EFAULT;
>
> I think the abort_ip check should have the same error value as the
> other sanity checks, ie just be of this format:
>
>> if (rseq_cs->version > 0)
>> return -EINVAL;
OK, so I'll go for -EINVAL.
>
> also, I think you should check start_ip to be consistent. You kind of
> accidentally do it with the check for
>
> if (rseq_cs->abort_ip - rseq_cs->start_ip - rseq_cs->post_commit_offset)
The check is actually:
/* Ensure that abort_ip is not in the critical section. */
if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
return -EINVAL;
>
> but honestly, that has underflow issues already, so I think you want
> to basically make the check be
>
> if (rseq_cs->abort_ip >= TASK_SIZE)
> return -EINVAL;
that works.
>
> if (rseq_cs->start_ip >= rseq_cs->abort_ip)
> return -EINVAL;
this one does not work. We need to ensure that abort_ip
is not between [ start_ip, start_ip + post_commit_offset ]. The
check you propose validates that start_ip is below abort_ip,
which is bogus. For instance, abort_ip can very well be in a
different section of the binary, at an address either below
or above start_ip.
>
> which takes care of checkint start_ip, and also the underflow for the
> post_commit_offset check.
What underflow issues are you concerned with ?
>
> If somebody is depending on negative offsets, then that
> post_commit_offset logic is already wrong.
>
>> + usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
>> ret = get_user(sig, usig);
>
> That can underflow too, but I guess we can just rely on get_user()
> getting it right.
Yes, get_user() should handle that one properly.
Thanks,
Mathieu
>
> Linus
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
