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    SubjectRe: question about /proc/<PID>/mem in 2.4
    On Tue, Jul 06, 2004 at 12:14:04PM +0100, Tigran Aivazian wrote:
    > On Mon, 5 Jul 2004, FabF wrote:
    > > > Surely, the super user (i.e. CAP_SYS_PTRACE in this context) should be
    > > > allowed to read any process' memory without having to do the
    > > > PTRACE_ATTACH/PTRACE_PEEKUSER kind of thing which strace(8) is doing?
    > >
    > > FYI may_ptrace_attach plugged somewhere between 2.4.21 & 22.This one get
    > > used as is (ie without MAY_PTRACE) in proc_pid_environ but dunno about
    > > reason why CAP_SYS_PTRACE isn't authoritative elsewhere.
    >
    > Ok, but still nobody seems to know why the super user is not allowed to
    > access /proc/<PID>/mem of any task. Any code which nobody in the world
    > knows the reason for, is broken and should be removed.
    >
    > I will wait a few weeks to see if someone does come up with the reason for
    > that "extra secure" check in mem_read() and if nobody has objections I'll
    > send Linus a patch to relax the check to a more reasonable one, namely to
    > allow CAP_SYS_PTRACE process to bypass any other conditions imposed.

    Hi Tigran,

    This code was added to stop the ptrace/kmod vulnerabilities. I do not
    fully understand the issues around tsk->is_dumpable and the fix itself,
    but I agree on that the checks here could be relaxed for the super user.

    However changing it to

    if (!is_dumpable(task) && !capable(CAP_SYS_PTRACE))
    goto out;

    Seems wrong because this will stop always honoring the tsk->is_dumpable flag. (?)

    Alan for sure can make the picture clear - he wrote this thing.


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