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

From: Manfred Spraul
Date: Sun Aug 20 2006 - 14:59:33 EST

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

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.


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