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Date: Fri, 06 Jun 2014 09:16:07 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexey Preobrazhensky <preobr@...gle.com>,
"netdev@...r.kernel.org" <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>,
dormando <dormando@...ia.net>
Subject: Re: Potential race in ip4_datagram_release_cb
On Fri, 2014-06-06 at 08:59 -0700, Alexei Starovoitov wrote:
> On Fri, Jun 6, 2014 at 5:56 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Fri, 2014-06-06 at 15:29 +0400, Alexey Preobrazhensky wrote:
> >> Hello,
> >>
> >> I’m working on AddressSanitizer[1] -- a tool that detects
> >> use-after-free and out-of-bounds bugs in kernel.
> >>
> >> We’ve encountered a heap-use-after-free in ip4_datagram_release_cb()
> >> in linux kernel 3.15-rc5 (revision
> >> 60b5f90d0fac7585f1a43ccdad06787b97eda0ab).
> >>
> >> It seems to be a race between dst_release() and
> >> ip4_datagram_release_cb() on an object from ip_dst_cache slab, all
> >> during the ip4_datagram_connect() call.
> >>
> >> This heap-use-after-free was triggered under trinity syscall fuzzer,
> >> so there is no reproducer.
> >>
> >> It would be great if someone familiar with the code took time to look
> >> into this report.
> >>
> >> Thanks,
> >> Alexey
> >>
> >> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
> >>
> >>
> >> AddressSanitizer: heap-use-after-free in ipv4_dst_check
> >> Read of size 2 by thread T15453:
> >> [<ffffffff817daa3a>] ipv4_dst_check+0x1a/0x90 ./net/ipv4/route.c:1116
> >> [<ffffffff8175b789>] __sk_dst_check+0x89/0xe0 ./net/core/sock.c:531
> >> [<ffffffff81830a36>] ip4_datagram_release_cb+0x46/0x390 ??:0
> >> [<ffffffff8175eaea>] release_sock+0x17a/0x230 ./net/core/sock.c:2413
> >> [<ffffffff81830882>] ip4_datagram_connect+0x462/0x5d0 ??:0
> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534
> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701
> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682
> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b
> >> ./arch/x86/kernel/entry_64.S:629
> >>
> >> Freed by thread T15455:
> >> [<ffffffff8178d9b8>] dst_destroy+0xa8/0x160 ./net/core/dst.c:251
> >> [<ffffffff8178de25>] dst_release+0x45/0x80 ./net/core/dst.c:280
> >> [<ffffffff818304c1>] ip4_datagram_connect+0xa1/0x5d0 ??:0
> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534
> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701
> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682
> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b
> >> ./arch/x86/kernel/entry_64.S:629
> >>
> >> Allocated by thread T15453:
> >> [<ffffffff8178d291>] dst_alloc+0x81/0x2b0 ./net/core/dst.c:171
> >> [<ffffffff817db3b7>] rt_dst_alloc+0x47/0x50 ./net/ipv4/route.c:1406
> >> [< inlined >] __ip_route_output_key+0x3e8/0xf70
> >> __mkroute_output ./net/ipv4/route.c:1939
> >> [<ffffffff817dde08>] __ip_route_output_key+0x3e8/0xf70 ./net/ipv4/route.c:2161
> >> [<ffffffff817deb34>] ip_route_output_flow+0x14/0x30 ./net/ipv4/route.c:2249
> >> [<ffffffff81830737>] ip4_datagram_connect+0x317/0x5d0 ??:0
> >> [<ffffffff81846d06>] inet_dgram_connect+0x76/0xd0 ./net/ipv4/af_inet.c:534
> >> [<ffffffff817580ac>] SYSC_connect+0x15c/0x1c0 ./net/socket.c:1701
> >> [<ffffffff817596ce>] SyS_connect+0xe/0x10 ./net/socket.c:1682
> >> [<ffffffff818b0a29>] system_call_fastpath+0x16/0x1b
> >> ./arch/x86/kernel/entry_64.S:629
> >>
> >> The buggy address ffff880024ff2266 is located 102 bytes inside
> >> of 192-byte region [ffff880024ff2200, ffff880024ff22c0)
> >>
> >> Memory state around the buggy address:
> >> ffff880024ff1d00: ffffffff fffrrrrr rrrrrrrr rrrrrrrr
> >> ffff880024ff1e00: ffffffff ffffffff ffffffff fffrrrrr
> >> ffff880024ff1f00: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr
> >> ffff880024ff2000: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr
> >> ffff880024ff2100: rrrrrrrr rrrrrrrr rrrrrrrr rrrrrrrr
> >> >ffff880024ff2200: ffffffff ffffffff ffffffff rrrrrrrr
> >> ^
> >> ffff880024ff2300: rrrrrrrr rrrrrrrr ........ ........
> >> ffff880024ff2400: ........ rrrrrrrr rrrrrrrr rrrrrrrr
> >> ffff880024ff2500: ffffffff ffffffff ffffffff rrrrrrrr
> >> ffff880024ff2600: rrrrrrrr rrrrrrrr ffffffff ffffffff
> >> ffff880024ff2700: ffffffff rrrrrrrr rrrrrrrr rrrrrrrr
> >> Legend:
> >> f - 8 freed bytes
> >> r - 8 redzone bytes
> >> . - 8 allocated bytes
> >> x=1..7 - x allocated bytes + (8-x) redzone bytes
> >> --
> >
> >
> > Yeah, we had many reports in the past that something was wrong ...
> >
> > Your nice report made me take a look, finally :(
> >
> > Problem comes from
> >
> > net/ipv4/udp.c:1008: sk_dst_set(sk, dst_clone(&rt->dst));
> >
> > Could you try following patch ?
> >
> > Thanks !
> >
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 4468e1adc094..d5e68ee63b8f 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1004,8 +1004,11 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
> > if ((rt->rt_flags & RTCF_BROADCAST) &&
> > !sock_flag(sk, SOCK_BROADCAST))
> > goto out;
> > - if (connected)
> > - sk_dst_set(sk, dst_clone(&rt->dst));
> > + if (connected) {
> > + spin_lock_bh(&sk->sk_lock.slock);
> > + __sk_dst_set(sk, dst_clone(&rt->dst));
> > + spin_unlock_bh(&sk->sk_lock.slock);
> > + }
>
> Nice catch.
> Should then we change sk_dst_set() itself to do spin_lock_bh unconditionally?
> Seems overhead is smaller, than checking all possible callsites manually.
>
> cc-ing Dormando as well.
Real problem is that sk_dst_set() uses a different lock. I never
understood how this was supposed to work.
We should either :
1) use xchg() and no lock at all to change sk_dst_cache, as we did for
sk_rx_dst ( cf udp_sk_rx_dst_set() )
2) No longer use sk_dst_lock, and always use the socket lock
(sk->sk_lock.slock) instead.
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