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    SubjectRe: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree
    On Wed, Feb 15, 2012 at 04:38:16PM +0100, Oleg Nesterov wrote:
    > >
    > > Wait, how it's differ from other ptrace_may_access calls all over
    > > the kernel? I suppose I'm missing something obvious?
    > For example? Say, mm_access() is fine because it returns ->mm
    > which we are going to play with.

    So, say we have

    success, and first reader continue here

    then say task change own credentials and all
    this sequence fails because access is not granted
    anymore (say for second reader), but first reader
    still able to continue reading because access was
    graned earlier.

    So I don't understand how it's different from what
    is provided in this patch. What I'm missing?

    > Once again, I am not saying that this code really has the security
    > problems. I simply do not know. But it looks wrong without the
    > comment. I do not really understand why do we need ptrace_may_access(),
    > but whatever reason we have how we can trust it? Say, when KCMP_VM
    > checks ->mm, all we know is that PTRACE_MODE_READ succeed in the
    > past. This looks confusing, imho.

    Adding the comment is not a problem. The problem is that I
    dont understand if there error in patch or not, can we stick
    with ptrace_may_access or need something different here?
    The idea was exactly like -- if you have enough rights to
    proceed ptrace_may_access then syscall should continue
    executing and return comparision result.


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