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    SubjectRe: [PATCH] getsockopt() early argument sanity checking
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    On Sunday 20 August 2006 18:16, Solar Designer wrote:
    > On Sun, Aug 20, 2006 at 10:34:43AM +0200, Andi Kleen wrote:
    > > In general I don't think it makes sense to submit stuff for 2.4
    > > that isn't in 2.6.
    >
    > In general I agree, however right now I had the choice between
    > submitting these changes for 2.4 first and not submitting them at all
    > (at least for some months more). I chose the former.

    If there is really a length checking bug it shouldn't be that hard to fix it
    in both.


    > 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).
    >
    > Of course, it is possible that I am wrong about some of the above;
    > please correct me if so.

    Nah you're right (except on a preemptible kernel which 2.4 isn't unpatched)
    However if there is any other user access before the second get_user
    the race could happen again even on UP.

    -Andi
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