Re: kernel BUG at include/linux/mm.h:LINE! (2)

[Eric Biggers]

On Fri, Jun 08, 2018 at 06:11:02AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    7170e6045a6a strparser: Add __strp_unpause and use it in k..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=114236af800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a601a80fec461d44
> dashboard link: https://syzkaller.appspot.com/bug?extid=3225ce21c0e9929bb9cf
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=10f44fdf800000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=110f636f800000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+3225ce21c0e9929bb9cf@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> flags: 0x2fffc0000000000()
> raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffff80
> raw: ffffea0006b29220 ffff88021fffac18 0000000000000003 0000000000000000
> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) <= 0)
> ------------[ cut here ]------------
> kernel BUG at include/linux/mm.h:853!
> invalid opcode: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 4545 Comm: syz-executor492 Not tainted 4.17.0-rc7+ #82
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:get_page include/linux/mm.h:853 [inline]
> RIP: 0010:do_tcp_sendpages+0x1879/0x1e60 net/ipv4/tcp.c:1002
> RSP: 0018:ffff8801c2a06f88 EFLAGS: 00010203
> RAX: 0000000000000000 RBX: ffff8801d972d580 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81a66c25 RDI: ffffed0038540de0
> RBP: ffff8801c2a071e8 R08: ffff8801b11d2480 R09: 0000000000000006
> R10: ffff8801b11d2480 R11: 0000000000000000 R12: 000000000000301d
> R13: ffffea0006b2621c R14: ffff8801ae5a6040 R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020008000 CR3: 0000000008c6a000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  tls_push_sg+0x25b/0x860 net/tls/tls_main.c:126
>  tls_push_record+0xae5/0x13e0 net/tls/tls_sw.c:266
>  tls_sw_push_pending_record+0x22/0x30 net/tls/tls_sw.c:276
>  tls_handle_open_record net/tls/tls_main.c:164 [inline]
>  tls_sk_proto_close+0x734/0xad0 net/tls/tls_main.c:264
>  inet_release+0x104/0x1f0 net/ipv4/af_inet.c:427
>  inet6_release+0x50/0x70 net/ipv6/af_inet6.c:459
>  sock_release+0x96/0x1b0 net/socket.c:594
>  sock_close+0x16/0x20 net/socket.c:1149
>  __fput+0x34d/0x890 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:243
>  task_work_run+0x1e4/0x290 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x1aee/0x2730 kernel/exit.c:865
>  do_group_exit+0x16f/0x430 kernel/exit.c:968
>  __do_sys_exit_group kernel/exit.c:979 [inline]
>  __se_sys_exit_group kernel/exit.c:977 [inline]
>  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:977
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x43f368
> RSP: 002b:00007ffd03500578 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043f368
> RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
> RBP: 00000000004bf448 R08: 00000000000000e7 R09: ffffffffffffffd0
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 00000000006d1180 R14: 0000000000000000 R15: 0000000000000000
> Code: ff ff 41 89 86 cc 08 00 00 e8 e4 07 05 00 e9 2c eb ff ff e8 ca 4b 27
> fb 48 8b bd b8 fd ff ff 48 c7 c6 40 0c 54 88 e8 77 72 54 fb <0f> 0b 48 89 85
> b8 fd ff ff e8 a9 4b 27 fb 48 8b 85 b8 fd ff ff
> RIP: get_page include/linux/mm.h:853 [inline] RSP: ffff8801c2a06f88
> RIP: do_tcp_sendpages+0x1879/0x1e60 net/ipv4/tcp.c:1002 RSP:
> ffff8801c2a06f88
> ---[ end trace 500a6e4fab99629c ]---
> 
> 
> ---
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> 

AFAICS this was fixed by this commit:

	commit d829e9c4112b52f4f00195900fd4c685f61365ab
	Author: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
	Date:   Sat Oct 13 02:45:59 2018 +0200

	    tls: convert to generic sk_msg interface

So telling syzbot:

#syz fix: tls: convert to generic sk_msg interface

The issue was that described in this comment in tls_sw_sendmsg():

                /* Open records defined only if successfully copied, otherwise
                 * we would trim the sg but not reset the open record frags.
                 */
                tls_ctx->pending_open_record_frags = true;

Basically, on sendmsg() to a TLS socket, if the message buffer was partially
unmapped, a TLS record would be marked as pending (and then tried to be sent at
sock_release() time) even though it had actually been discarded.

- Eric