Date:   Wed, 1 Mar 2017 15:34:54 -0800
From:   Joe Stringer <joe@....org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH net] ipv6: orphan skbs in reassembly unit

On 1 March 2017 at 14:45, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Andrey reported a use-after-free in IPv6 stack.
>
> Issue here is that we free the socket while it still has skb
> in TX path and in some queues.
>
> It happens here because IPv6 reassembly unit messes skb->truesize,
> breaking skb_set_owner_w() badly.
>
> We fixed a similar issue for IPV4 in commit 8282f27449bf ("inet: frag:
> Always orphan skbs inside ip_defrag()")
>
> ==================================================================
> BUG: KASAN: use-after-free in sock_wfree+0x118/0x120
> Read of size 8 at addr ffff880062da0060 by task a.out/4140
>
> page:ffffea00018b6800 count:1 mapcount:0 mapping:          (null)
> index:0x0 compound_mapcount: 0
> flags: 0x100000000008100(slab|head)
> raw: 0100000000008100 0000000000000000 0000000000000000 0000000180130013
> raw: dead000000000100 dead000000000200 ffff88006741f140 0000000000000000
> page dumped because: kasan: bad access detected
>
> CPU: 0 PID: 4140 Comm: a.out Not tainted 4.10.0-rc3+ #59
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15
>  dump_stack+0x292/0x398 lib/dump_stack.c:51
>  describe_address mm/kasan/report.c:262
>  kasan_report_error+0x121/0x560 mm/kasan/report.c:370
>  kasan_report mm/kasan/report.c:392
>  __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:413
>  sock_flag ./arch/x86/include/asm/bitops.h:324
>  sock_wfree+0x118/0x120 net/core/sock.c:1631
>  skb_release_head_state+0xfc/0x250 net/core/skbuff.c:655
>  skb_release_all+0x15/0x60 net/core/skbuff.c:668
>  __kfree_skb+0x15/0x20 net/core/skbuff.c:684
>  kfree_skb+0x16e/0x4e0 net/core/skbuff.c:705
>  inet_frag_destroy+0x121/0x290 net/ipv4/inet_fragment.c:304
>  inet_frag_put ./include/net/inet_frag.h:133
>  nf_ct_frag6_gather+0x1125/0x38b0 net/ipv6/netfilter/nf_conntrack_reasm.c:617
>  ipv6_defrag+0x21b/0x350 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68
>  nf_hook_entry_hookfn ./include/linux/netfilter.h:102
>  nf_hook_slow+0xc3/0x290 net/netfilter/core.c:310
>  nf_hook ./include/linux/netfilter.h:212
>  __ip6_local_out+0x52c/0xaf0 net/ipv6/output_core.c:160
>  ip6_local_out+0x2d/0x170 net/ipv6/output_core.c:170
>  ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1722
>  ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1742
>  rawv6_push_pending_frames net/ipv6/raw.c:613
>  rawv6_sendmsg+0x2cff/0x4130 net/ipv6/raw.c:927
>  inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
>  sock_sendmsg_nosec net/socket.c:635
>  sock_sendmsg+0xca/0x110 net/socket.c:645
>  sock_write_iter+0x326/0x620 net/socket.c:848
>  new_sync_write fs/read_write.c:499
>  __vfs_write+0x483/0x760 fs/read_write.c:512
>  vfs_write+0x187/0x530 fs/read_write.c:560
>  SYSC_write fs/read_write.c:607
>  SyS_write+0xfb/0x230 fs/read_write.c:599
>  entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203
> RIP: 0033:0x7ff26e6f5b79
> RSP: 002b:00007ff268e0ed98 EFLAGS: 00000206 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007ff268e0f9c0 RCX: 00007ff26e6f5b79
> RDX: 0000000000000010 RSI: 0000000020f50fe1 RDI: 0000000000000003
> RBP: 00007ff26ebc1220 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
> R13: 00007ff268e0f9c0 R14: 00007ff26efec040 R15: 0000000000000003
>
> The buggy address belongs to the object at ffff880062da0000
>  which belongs to the cache RAWv6 of size 1504
> The buggy address ffff880062da0060 is located 96 bytes inside
>  of 1504-byte region [ffff880062da0000, ffff880062da05e0)
>
> Freed by task 4113:
>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:502
>  set_track mm/kasan/kasan.c:514
>  kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:578
>  slab_free_hook mm/slub.c:1352
>  slab_free_freelist_hook mm/slub.c:1374
>  slab_free mm/slub.c:2951
>  kmem_cache_free+0xb2/0x2c0 mm/slub.c:2973
>  sk_prot_free net/core/sock.c:1377
>  __sk_destruct+0x49c/0x6e0 net/core/sock.c:1452
>  sk_destruct+0x47/0x80 net/core/sock.c:1460
>  __sk_free+0x57/0x230 net/core/sock.c:1468
>  sk_free+0x23/0x30 net/core/sock.c:1479
>  sock_put ./include/net/sock.h:1638
>  sk_common_release+0x31e/0x4e0 net/core/sock.c:2782
>  rawv6_close+0x54/0x80 net/ipv6/raw.c:1214
>  inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
>  inet6_release+0x50/0x70 net/ipv6/af_inet6.c:431
>  sock_release+0x8d/0x1e0 net/socket.c:599
>  sock_close+0x16/0x20 net/socket.c:1063
>  __fput+0x332/0x7f0 fs/file_table.c:208
>  ____fput+0x15/0x20 fs/file_table.c:244
>  task_work_run+0x19b/0x270 kernel/task_work.c:116
>  exit_task_work ./include/linux/task_work.h:21
>  do_exit+0x186b/0x2800 kernel/exit.c:839
>  do_group_exit+0x149/0x420 kernel/exit.c:943
>  SYSC_exit_group kernel/exit.c:954
>  SyS_exit_group+0x1d/0x20 kernel/exit.c:952
>  entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203
>
> Allocated by task 4115:
>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:502
>  set_track mm/kasan/kasan.c:514
>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:605
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:544
>  slab_post_alloc_hook mm/slab.h:432
>  slab_alloc_node mm/slub.c:2708
>  slab_alloc mm/slub.c:2716
>  kmem_cache_alloc+0x1af/0x250 mm/slub.c:2721
>  sk_prot_alloc+0x65/0x2a0 net/core/sock.c:1334
>  sk_alloc+0x105/0x1010 net/core/sock.c:1396
>  inet6_create+0x44d/0x1150 net/ipv6/af_inet6.c:183
>  __sock_create+0x4f6/0x880 net/socket.c:1199
>  sock_create net/socket.c:1239
>  SYSC_socket net/socket.c:1269
>  SyS_socket+0xf9/0x230 net/socket.c:1249
>  entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:203
>
> Memory state around the buggy address:
>  ffff880062d9ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff880062d9ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>ffff880062da0000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                        ^
>  ffff880062da0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff880062da0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

For reference, I suggested a very similar change last year:
https://patchwork.ozlabs.org/patch/610116/

At that time, I linked it to this commit:
Fixes: 029f7f3b8701 ("netfilter: ipv6: nf_defrag: avoid/free clone operations")

I'm happy with the change from OVS side.

Acked-by: Joe Stringer <joe@....org>

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