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    SubjectRe: [patch 3/3] [PATCH] prctl: Add PR_SET_MM codes to set up mm_struct entires v3
    On Mon, Dec 12, 2011 at 04:49:38PM -0500, KOSAKI Motohiro wrote:
    > Hi
    >
    > > When we restore a task we need to set up text, data and data
    > > heap sizes from userspace to the values a task had at
    > > checkpoint time. This patch adds auxilary prctl codes for that.
    > >
    > > While most of them have a statistical nature (their values
    > > are involved into calculation of /proc/<pid>/statm output)
    > > the start_brk and brk values are used to compute an allowed
    > > size of program data segment expansion. Which means an arbitrary
    > > changes of this values might be dangerous operation. So to restrict
    > > access the following requirements applied to prctl calls:
    > >
    > > - The process has to have CAP_SYS_ADMIN capability granted.
    >
    > This is very dangerous feature and useless from regular admins.

    Except brk() call I don't see where it might be extremelly
    dangerous at moment but indeed it might become very dangerous
    once code grows. Still if evil minded person got CAP_SYS_ADMIN
    these prctls are least thing one should carry about.

    > Moreover, CAP_SYS_ADMIN has a pretty overweight meanings and
    > we can't disable it on practical. So, I have a question. Why
    > don't you make new capability for checkpoint?
    >

    It's not a problem to introduce CAP_CHECKPOINT_RESTORE, but
    would it be accepted? I mean, are we fine with new capability
    introduction? If yes -- I'll add new one and rebase the patch.

    Cyrill


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