netdev - Re: [PATCH] ipv4: fix a race in ip4_datagram_release

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Date:	Wed, 11 Jun 2014 05:41:02 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	dormando <dormando@...ia.net>
Cc:	Alexey Preobrazhensky <preobr@...gle.com>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	David Miller <davem@...emloft.net>, paulmck@...ux.vnet.ibm.com,
	netdev@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Lars Bull <larsbull@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Bruce Curtis <brutus@...gle.com>,
	Maciej Żenczykowski <maze@...gle.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH] ipv4: fix a race in ip4_datagram_release_cb()

On Wed, 2014-06-11 at 00:38 -0700, dormando wrote:
> On Wed, 11 Jun 2014, dormando wrote:
> >
> > --> Meant to say here that both *with* and *without* your two new patches
> > it still crashes.
> >
> > > Unfortunately 3.14 has a few regressions.. one is some bad CPU usage i'll
> > > have to track down, and two something about pstore is broken, so I can't
> > > get the trace from the crash. It's compressing now and has more of the
> > > kernel log, but it's missing the actual panic part.
> > >
> > > $ git log --oneline v3.14..v3.15 net/ipv4/route.c
> > > fbdc0ad ipv4: initialise the itag variable in __mkroute_input
> > > 0d5edc6 ipv4, route: pass 0 instead of LOOPBACK_IFINDEX to fib_validate_source()
> > > aad8872 ipv4: add a sock pointer to dst->output() path.
> > > 9114615 ipv4: return valid RTA_IIF on ip route get
> > > 3ed66e9 net: replace __this_cpu_inc in route.c with raw_cpu_inc
> > > 0b8c7f6 ipv4: remove ip_rt_dump from route.c
> > > 4a4eb21 ipv4: remove ipv4_ifdown_dst from route.c
> > > 1e8d642 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
> > > 2045cea net: remove unnecessary return's
> > >
> > > No more obvious race fixes. I can try 3.15 fully vanilla but I'm having
> > > doubts?
> > >
> > > We have a few patches on top of this, but none of them are active at the
> > > time of my test. I've tried removing them in the past and it did nothing
> > > as well.
> > >
> > > Sorry :(
> > >
> 
> Spamming now! The pstore'd dmesg looked suspiciously like the boot before
> I booted the crashed kernel.. checked pstore again and the crash is there
> after a second reboot (wtf.. will test tomorrow).


OK then we probably have another bug in UDP, which is that we call
sk_dst_set(sk, dst_clone(&rt->dst)); with a dst having DST_NOCACHE set

Its a problem, because sk_dst_get() cannot deal safely with such dst.

Care to share your program triggering the bug ?



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