Re: [MPTCP] KASAN: use-after-free Read in mptcp_established_options

[Paolo Abeni]

On Wed, 2021-02-17 at 09:30 -0800, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    966df6de lan743x: sync only the received area of an rx rin..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11afe082d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=dbc1ca9e55dc1f9f
> dashboard link: https://syzkaller.appspot.com/bug?extid=3c1e5ab4997849b69807
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3c1e5ab4997849b69807@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in mptcp_check_fallback net/mptcp/protocol.h:745 [inline]
> BUG: KASAN: use-after-free in mptcp_established_options+0x22cf/0x2780 net/mptcp/options.c:724
> Read of size 8 at addr ffff88802bea10a0 by task syz-executor.1/11042
> 
> CPU: 1 PID: 11042 Comm: syz-executor.1 Not tainted 5.11.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  __kasan_report mm/kasan/report.c:396 [inline]
>  kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
>  mptcp_check_fallback net/mptcp/protocol.h:745 [inline]
>  mptcp_established_options+0x22cf/0x2780 net/mptcp/options.c:724
>  tcp_established_options+0x4ed/0x700 net/ipv4/tcp_output.c:953
>  tcp_current_mss+0x1d2/0x360 net/ipv4/tcp_output.c:1840
>  tcp_send_mss+0x28/0x2b0 net/ipv4/tcp.c:943
>  mptcp_sendmsg_frag+0x13b/0x1220 net/mptcp/protocol.c:1266
>  mptcp_push_pending+0x2cc/0x650 net/mptcp/protocol.c:1477
>  mptcp_sendmsg+0xde4/0x2830 net/mptcp/protocol.c:1685
>  inet6_sendmsg+0x99/0xe0 net/ipv6/af_inet6.c:642
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  sock_write_iter+0x289/0x3c0 net/socket.c:999
>  call_write_iter include/linux/fs.h:1901 [inline]
>  new_sync_write+0x426/0x650 fs/read_write.c:518
>  vfs_write+0x791/0xa30 fs/read_write.c:605
>  ksys_write+0x1ee/0x250 fs/read_write.c:658
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x465d99
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ff231ccc188 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 000000000056c008 RCX: 0000000000465d99
> RDX: 000000000003f9b4 RSI: 0000000020000000 RDI: 0000000000000004
> RBP: 00000000004bcf27 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056c008
> R13: 00007ffeaa2da27f R14: 00007ff231ccc300 R15: 0000000000022000
> 
> Allocated by task 11017:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:401 [inline]
>  ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:429
>  kmalloc include/linux/slab.h:552 [inline]
>  kzalloc include/linux/slab.h:682 [inline]
>  subflow_create_ctx+0x82/0x230 net/mptcp/subflow.c:1378
>  subflow_ulp_init+0x62/0x370 net/mptcp/subflow.c:1459
>  __tcp_set_ulp net/ipv4/tcp_ulp.c:139 [inline]
>  tcp_set_ulp+0x27c/0x610 net/ipv4/tcp_ulp.c:160
>  mptcp_subflow_create_socket+0x5bf/0xe20 net/mptcp/subflow.c:1343
>  __mptcp_socket_create net/mptcp/protocol.c:110 [inline]
>  mptcp_init_sock net/mptcp/protocol.c:2365 [inline]
>  mptcp_init_sock+0x140/0x830 net/mptcp/protocol.c:2350
>  inet6_create net/ipv6/af_inet6.c:256 [inline]
>  inet6_create+0xa15/0x1010 net/ipv6/af_inet6.c:110
>  __sock_create+0x3de/0x780 net/socket.c:1406
>  sock_create net/socket.c:1457 [inline]
>  __sys_socket+0xef/0x200 net/socket.c:1499
>  __do_sys_socket net/socket.c:1508 [inline]
>  __se_sys_socket net/socket.c:1506 [inline]
>  __x64_sys_socket+0x6f/0xb0 net/socket.c:1506
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 10650:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
>  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:356
>  ____kasan_slab_free+0xe1/0x110 mm/kasan/common.c:362
>  kasan_slab_free include/linux/kasan.h:192 [inline]
>  slab_free_hook mm/slub.c:1547 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1580
>  slab_free mm/slub.c:3143 [inline]
>  kmem_cache_free_bulk mm/slub.c:3269 [inline]
>  kmem_cache_free_bulk+0x253/0xc80 mm/slub.c:3256
>  kfree_bulk include/linux/slab.h:409 [inline]
>  kfree_rcu_work+0x4cd/0x860 kernel/rcu/tree.c:3226
>  process_one_work+0x98d/0x15f0 kernel/workqueue.c:2275
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>  kthread+0x3b1/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> 
> The buggy address belongs to the object at ffff88802bea1000
>  which belongs to the cache kmalloc-256 of size 256
> The buggy address is located 160 bytes inside of
>  256-byte region [ffff88802bea1000, ffff88802bea1100)
> The buggy address belongs to the page:
> page:0000000026103328 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2bea0
> head:0000000026103328 order:1 compound_mapcount:0
> flags: 0xfff00000010200(slab|head)
> raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010c413c0
> raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff88802bea0f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88802bea1000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff88802bea1080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                ^
>  ffff88802bea1100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88802bea1180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================

very likely

#syz dup: WARNING in dst_release

(same root cause, we need to clear msk->first when the relevant subflow
is disposed by the workqueue)

/P