Re: [PATCH] audit: grab a reference to context->pwd when it's cached

Peter Moody
2012-10-05T15:17:16Z

On Fri, Oct 5, 2012 at 7:26 AM, Jeff Layton <jlayton@redhat.com> wrote:
> On Fri, 5 Oct 2012 06:57:59 -0700
> Peter Moody <pmoody@google.com> wrote:
>
>> On Fri, Oct 5, 2012 at 5:55 AM, Jeff Layton <jlayton@redhat.com> wrote:
>> > On Thu, 4 Oct 2012 11:48:23 -0700
>> > Peter Moody <pmoody@google.com> wrote:
>> >
>> >> On Wed, Sep 26, 2012 at 6:50 AM, Alexander Viro <aviro@redhat.com> wrote:
>> >> > On Tue, Sep 25, 2012 at 10:03:23AM -0700, Peter Moody wrote:
>> >> >> Hey folks,
>> >> >>
>> >> >> following up on old patches, are there any comments on this? Did you
>> >> >> get around to finding a better way to fix this bug, Al?
>> >> >
>> >> > Alas, I've found none ;-/ Looks like we'll have to go with this one,
>> >> > at least until somebody comes up with better solution.
>> >>
>> >> Not surprisingly, this patch doesn't actually fix the issue (or at
>> >> least doesn't do it correctly).
>> >>
>> >> I hadn't noticed that get_fs_pwd() actually calls path_get() on
>> >> &context->pwd so the additional path_get() is useless and the
>> >> reference doesn't ever actually get freed if audit_putname is called
>> >> while we're in a syscall.
>> >>
>> >> Al, Eric, Jeff; do any of you guys have an understanding of what the
>> >> initial bug actually is since this clearly doesn't fix it?
>> >>
>> >> Cheers,
>> >> peter
>> >>
>> >
>> > BTW, I ran this test on one of my KVM guests and it ran just fine. That
>> > one is an x86_64 guest running a 3.6.0+ kernel. The root fs on there is
>> > ext4 though, not ext3. So perhaps that's a factor?
>> >
>> > The oops message you posted at least looks like something down in the
>> > bowels of ext3 or fs/buffer.c.
>>
>> Yeah, the only place this actually happens for me on these giant xen
>> instances we have (6 cores, 32G ram) and it happens on both ext3 and
>> ext4 filesystems and it happens with 100% reliability.
>>
>> The actual oops is from:
>>
>> static inline void check_irqs_on(void)
>> {
>> #ifdef irqs_disabled
>> BUG_ON(irqs_disabled());
>> #endif
>> }
>>
>> with the code path looking like:
>>
>> __find_get_block() -> lookup_bh_lru() -> check_irqs_on() -> BUG()
>>
>
> Do you have a backtrace from a more recent kernel? I wonder if
> something in the syscall exit codepath is disabling IRQs here?

is 3.6.0-rc1 recent enough or do you want something newer?

> --
> Jeff Layton <jlayton@redhat.com>