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

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Date:	Sun, 20 Aug 2006 18:30:51 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Solar Designer <solar@...nwall.com>
Cc:	Andi Kleen <ak@...e.de>, Willy Tarreau <wtarreau@...a.kernel.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] getsockopt() early argument sanity checking


> 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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