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    SubjectRe: Posix file capabilities in 2.6.24rc2; now 2.6.24-rc3
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    Serge E. Hallyn wrote:
    > The problem is that when you run a setuid binary, its pP and pE are
    > fully raised. The following patch fixes it for me. Chris, does it fix
    > your problem? Andrew, am I again confusing myself and doing something
    > unsafe?

    I think this is yet another example of the fragile mess that is UID
    emulation with capabilities. Your patch is an example of privilege
    escalation - luser can kill a more-capable process. In the kill CONT
    case we reached the opposite conclusion to this one. As was the case
    then, I didn't disagree then :*). If it meets folk's expectations, then
    this is probably a good patch...

    > --- a/security/commoncap.c
    > +++ b/security/commoncap.c
    > @@ -543,6 +543,9 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
    > if (capable(CAP_KILL))
    > return 0;
    >
    > + if (p->euid==0 && p->uid==current->uid)
    > + return 0;
    > +

    Its late and I'm obviously tired, but is there any reason not to simply use:

    if (p->uid == current->uid)
    return 0;

    Whatever the case, could you put the new code closer to the sig ==
    SIGCONT test? The capability tests are at the end of cap_task_kill() and
    this new check breaks that pattern.

    Cheers

    Andrew
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