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    SubjectRe: vfs: INFO: possible circular locking dependency detected
    On Wed, May 09, 2012 at 05:28:54PM +0100, Al Viro wrote:
    > On Wed, May 09, 2012 at 06:23:30PM +0200, Sasha Levin wrote:
    > > On Wed, May 9, 2012 at 6:12 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
    > > > On Wed, May 09, 2012 at 05:25:14PM +0200, Sasha Levin wrote:
    > > >> Hi all,
    > > >>
    > > >> I've started seeing the following warning while fuzzing inside a KVM guest with the latest -next:
    > > > ? ? ? ?It's not a realistic attack, fortunately, since you need root
    > > > to get past open_exec() on any of those... ?Wait. ?How _did_ you get
    > > > past open_exec(), anyway? ?MAY_EXEC is not supposed to be granted on
    > > > anything that has no exec bits at all and AFAICS none of those files
    > > > have them.
    > >
    > > You could chmod +x and run them, no?
    >
    > Can't. proc_setattr() will give you -EPERM and refuse to do anything
    > if you call it with ATTR_MODE in ->ia_valid.

    OTOH, you probably can do that on unrelated seq_file outside of per-process
    part of procfs. So, yes, one could get a warning like that if they, as root,
    would do e.g.
    chmod +x /proc/swaps
    attempt to execve() /proc/swaps
    cat /proc/self/environ
    and enjoy the hard-earned false positive (it's a different seq_file, so
    we have no deadlock). If that's _all_ that happened, I'm not particulary
    concerned; it's not pretty, but saying "thou shalt not grab ->cred_guard_mutex
    anywhere in ->read() on anything that has exec bits or might get one" is
    not too terrible. If that's something else, though, we might have a real
    problem...


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