Re: [PATCH] getsockopt() early argument sanity checking

Manfred Spraul
2006-08-20T18:58:30Z

Arjan wrote:

>> We're on UP. sys_getsockopt() does get_user() (due to the patch) and
>> makes sure that the passed *optlen is sane. Even if this get_user()
>> sleeps, the value it returns in "len" is what's currently in memory at
>> the time of the get_user() return (correct?) Then an underlying
>> *getsockopt() function does another get_user() on optlen (same address),
>> without doing any other user-space data accesses or anything else that
>> could sleep first. Is it possible that this second get_user()
>> invocation would sleep? I think not since it's the same address that
>> we've just read a value from, we did not leave kernel space, and we're
>> on UP (so no other processor could have changed the mapping). So the
>> patch appears to be sufficient for this special case (which is not
>> unlikely).
>
>this reasoning goes out the window with kernel preemption of course ;)
>
>
Or O_DIRECT? I'm not sure what's easier to time, a kernel preemption or
a DMA to the user address.

--
Manfred