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

From: Arjan van de Ven
Date: Sun Aug 20 2006 - 12:29:10 EST

> 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 ;)

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