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Date: Fri, 6 Jun 2014 08:59:56 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Eric Dumazet <eric.dumazet@...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, 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.
> }
>
> if (msg->msg_flags&MSG_CONFIRM)
>
>
> --
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