Re: KASAN: out-of-bounds Write in tls_push_record

[Eric Biggers]

On Sat, Jul 07, 2018 at 06:29:03PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    526674536360 Add linux-next specific files for 20180706
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=17e63968400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c8d1cfc0cb798e48
> dashboard link: https://syzkaller.appspot.com/bug?extid=43358359519ad16cf05e
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=15790594400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12b53f48400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+43358359519ad16cf05e@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> RDX: 00000000fffffdef RSI: 00000000200005c0 RDI: 0000000000000004
> RBP: 00000000006cb018 R08: 0000000020000000 R09: 000000000000001c
> R10: 0000000000000040 R11: 0000000000000216 R12: 0000000000000005
> R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
> ==================================================================
> BUG: KASAN: out-of-bounds in tls_fill_prepend include/net/tls.h:339 [inline]
> BUG: KASAN: out-of-bounds in tls_push_record+0x1091/0x1400
> net/tls/tls_sw.c:239
> Write of size 1 at addr ffff8801c07b8000 by task syz-executor985/4467
> 
> CPU: 0 PID: 4467 Comm: syz-executor985 Not tainted 4.18.0-rc3-next-20180706+
> #1
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>  __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
>  tls_fill_prepend include/net/tls.h:339 [inline]
>  tls_push_record+0x1091/0x1400 net/tls/tls_sw.c:239
>  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+0x74c/0xae0 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+0xd7/0x260 net/socket.c:600
>  sock_close+0x19/0x20 net/socket.c:1151
>  __fput+0x35d/0x930 fs/file_table.c:215
>  ____fput+0x15/0x20 fs/file_table.c:251
>  task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x1b08/0x2750 kernel/exit.c:869
>  do_group_exit+0x177/0x440 kernel/exit.c:972
>  __do_sys_exit_group kernel/exit.c:983 [inline]
>  __se_sys_exit_group kernel/exit.c:981 [inline]
>  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:981
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x43f358
> Code: Bad RIP value.
> RSP: 002b:00007ffd4c2414b8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043f358
> RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
> RBP: 00000000004bf448 R08: 00000000000000e7 R09: ffffffffffffffd0
> R10: 0000000000000040 R11: 0000000000000246 R12: 0000000000000001
> R13: 00000000006d1180 R14: 0000000000000000 R15: 0000000000000000
> 
> The buggy address belongs to the page:
> page:ffffea000701ee00 count:0 mapcount:-128 mapping:0000000000000000
> index:0x0
> flags: 0x2fffc0000000000()
> raw: 02fffc0000000000 ffffea0006b7be08 ffff88021fffac18 0000000000000000
> raw: 0000000000000000 0000000000000003 00000000ffffff7f 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801c07b7f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>  ffff8801c07b7f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > ffff8801c07b8000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>                       ^
>  ffff8801c07b8080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>  ffff8801c07b8100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ==================================================================
> 
> 
> ---
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> 
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> 

(As with the other reports of this...)

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