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

On Fri, Oct 5, 2012 at 7:26 AM, Jeff Layton <jlayton(a)redhat.com&gt; wrote: > On Fri, 5 Oct 2012 06:57:59 -0700 > Peter Moody <pmoody(a)google.com&gt; wrote: > >> On Fri, Oct 5, 2012 at 5:55 AM, Jeff Layton <jlayton(a)redhat.com&gt; wrote: >> > On Thu, 4 Oct 2012 11:48:23 -0700 >> > Peter Moody <pmoody(a)google.com&gt; wrote: >> > >> >> On Wed, Sep 26, 2012 at 6:50 AM, Alexander Viro <aviro(a)redhat.com&gt; 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(a)redhat.com&gt; -- Peter Moody Google 1.650.253.7306 Security Engineer pgp:0xC3410038