Date:   Mon, 19 Nov 2018 17:57:33 +0900
From:   Xin Long <lucien.xin@...il.com>
To:     syzbot+9276d76e83e3bcde6c99@...kaller.appspotmail.com
Cc:     davem <davem@...emloft.net>, LKML <linux-kernel@...r.kernel.org>,
        linux-sctp@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        network dev <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs@...glegroups.com,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: KASAN: use-after-free Read in __lock_sock

On Sat, Nov 17, 2018 at 4:18 PM syzbot
<syzbot+9276d76e83e3bcde6c99@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    ccda4af0f4b9 Linux 4.20-rc2
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=156cd533400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4a0a89f12ca9b0f5
> dashboard link: https://syzkaller.appspot.com/bug?extid=9276d76e83e3bcde6c99
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+9276d76e83e3bcde6c99@...kaller.appspotmail.com
>
> netlink: 5 bytes leftover after parsing attributes in process
> `syz-executor5'.
> ==================================================================
> BUG: KASAN: use-after-free in __lock_acquire+0x36d9/0x4c20
> kernel/locking/lockdep.c:3218
> Read of size 8 at addr ffff8881d26d60e0 by task syz-executor1/13725
>
> CPU: 0 PID: 13725 Comm: syz-executor1 Not tainted 4.20.0-rc2+ #333
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x244/0x39d lib/dump_stack.c:113
>   print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
>   kasan_report_error mm/kasan/report.c:354 [inline]
>   kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
>   __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>   __lock_acquire+0x36d9/0x4c20 kernel/locking/lockdep.c:3218
>   lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
>   __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
>   _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168
>   spin_lock_bh include/linux/spinlock.h:334 [inline]
>   __lock_sock+0x203/0x350 net/core/sock.c:2253
>   lock_sock_nested+0xfe/0x120 net/core/sock.c:2774
>   lock_sock include/net/sock.h:1492 [inline]
>   sctp_sock_dump+0x122/0xb20 net/sctp/diag.c:324

static int sctp_sock_dump(struct sctp_transport *tsp, void *p)
{
        struct sctp_endpoint *ep = tsp->asoc->ep;
        struct sctp_comm_param *commp = p;
        struct sock *sk = ep->base.sk; <--- [1]
...
        int err = 0;

        lock_sock(sk);  <--- [2]

Between [1] and [2], an asoc peeloff may happen, still thinking
how to avoid this.



>   sctp_for_each_transport+0x2b5/0x370 net/sctp/socket.c:5091
>   sctp_diag_dump+0x3ac/0x660 net/sctp/diag.c:527
>   __inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049
>   inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065
>   netlink_dump+0x606/0x1080 net/netlink/af_netlink.c:2244
>   __netlink_dump_start+0x59a/0x7c0 net/netlink/af_netlink.c:2352
>   netlink_dump_start include/linux/netlink.h:216 [inline]
>   inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170
>   __sock_diag_cmd net/core/sock_diag.c:232 [inline]
>   sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263
>   netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477
>   sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274
>   netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
>   netlink_unicast+0x5a5/0x760 net/netlink/af_netlink.c:1336
>   netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
>   sock_sendmsg_nosec net/socket.c:621 [inline]
>   sock_sendmsg+0xd5/0x120 net/socket.c:631
>   sock_write_iter+0x35e/0x5c0 net/socket.c:900
>   call_write_iter include/linux/fs.h:1857 [inline]
>   do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
>   do_iter_write+0x185/0x5f0 fs/read_write.c:959
>   vfs_writev+0x1f1/0x360 fs/read_write.c:1004
>   do_writev+0x11a/0x310 fs/read_write.c:1039
>   __do_sys_writev fs/read_write.c:1112 [inline]
>   __se_sys_writev fs/read_write.c:1109 [inline]
>   __x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457569
> Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f2cdabbac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
> RDX: 0000000000000001 RSI: 000000002051c000 RDI: 000000000000000e
> RBP: 000000000072c0e0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2cdabbb6d4
> R13: 00000000004c33b1 R14: 00000000004d97c8 R15: 00000000ffffffff
>
> Allocated by task 13672:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>   kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>   kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
>   sk_prot_alloc+0x69/0x2e0 net/core/sock.c:1463
>   sk_alloc+0x10d/0x1690 net/core/sock.c:1523
>   inet_create+0x509/0x1070 net/ipv4/af_inet.c:321
>   __sock_create+0x536/0x930 net/socket.c:1277
>   sock_create net/socket.c:1317 [inline]
>   __sys_socket+0x106/0x260 net/socket.c:1347
>   __do_sys_socket net/socket.c:1356 [inline]
>   __se_sys_socket net/socket.c:1354 [inline]
>   __x64_sys_socket+0x73/0xb0 net/socket.c:1354
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 13680:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>   kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>   __cache_free mm/slab.c:3498 [inline]
>   kmem_cache_free+0x83/0x290 mm/slab.c:3760
>   sk_prot_free net/core/sock.c:1504 [inline]
>   __sk_destruct+0x728/0xa80 net/core/sock.c:1588
>   sk_destruct+0x78/0x90 net/core/sock.c:1596
>   __sk_free+0xcf/0x300 net/core/sock.c:1607
>   sk_free+0x42/0x50 net/core/sock.c:1618
>   sock_put include/net/sock.h:1693 [inline]
>   sctp_close+0x8d4/0xad0 net/sctp/socket.c:1569
>   inet_release+0x104/0x1f0 net/ipv4/af_inet.c:428
>   __sock_release+0xd7/0x250 net/socket.c:579
>   sock_close+0x19/0x20 net/socket.c:1141
>   __fput+0x385/0xa30 fs/file_table.c:278
>   ____fput+0x15/0x20 fs/file_table.c:309
>   task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
>   get_signal+0x1558/0x1980 kernel/signal.c:2347
>   do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
>   exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8881d26d6040
>   which belongs to the cache SCTP(33:syz1) of size 1776
> The buggy address is located 160 bytes inside of
>   1776-byte region [ffff8881d26d6040, ffff8881d26d6730)
> The buggy address belongs to the page:
> page:ffffea000749b580 count:1 mapcount:0 mapping:ffff8881b517f200 index:0x0
> flags: 0x2fffc0000000200(slab)
> raw: 02fffc0000000200 ffff8881c6685748 ffffea0007538388 ffff8881b517f200
> raw: 0000000000000000 ffff8881d26d6040 0000000100000002 ffff8881b6b4e7c0
> page dumped because: kasan: bad access detected
> page->mem_cgroup:ffff8881b6b4e7c0
>
> Memory state around the buggy address:
>   ffff8881d26d5f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff8881d26d6000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> > ffff8881d26d6080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                         ^
>   ffff8881d26d6100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8881d26d6180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.

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