Re: KASAN: use-after-free Write in tls_push_record (2)

[Eric Biggers]

On Thu, Jul 12, 2018 at 06:44:55AM -0400, Boris Pismenny wrote:
> It seems to me that the crash here is due to write_space being called after
> the close system call. Maybe the correct solution is to move the TX software
> state to be released in sk_destruct. As we already do for the device state
> (see tls_device.c).
> 
> Is anyone looking into this one?
> 
> On 7/11/2018 8:49 PM, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following crash on:
> > 
> > HEAD commit:    1e09177acae3 Merge tag 'mips_fixes_4.18_3' of
> > git://git.ke..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=128903b2400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
> > dashboard link:
> > https://syzkaller.appspot.com/bug?extid=6c4e6ecbf9a2797be67c
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12312678400000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13ef76c2400000
> > 
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+6c4e6ecbf9a2797be67c@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 
> > RDX: 00000000fffffdef RSI: 00000000200005c0 RDI: 0000000000000003
> > RBP: 00000000006cb018 R08: 0000000020000000 R09: 000000000000001c
> > R10: 0000000000000040 R11: 0000000000000212 R12: 0000000000000005
> > R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
> > ==================================================================
> > BUG: KASAN: use-after-free in tls_fill_prepend include/net/tls.h:339
> > [inline]
> > BUG: KASAN: use-after-free in tls_push_record+0x1091/0x1400
> > net/tls/tls_sw.c:239
> > Write of size 1 at addr ffff8801ae430000 by task syz-executor589/4567
> > 
> > CPU: 0 PID: 4567 Comm: syz-executor589 Not tainted 4.18.0-rc4+ #141
> > 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+0x242/0x2fe 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:599
> >   sock_close+0x19/0x20 net/socket.c:1150
> >   __fput+0x355/0x8b0 fs/file_table.c:209
> >   ____fput+0x15/0x20 fs/file_table.c:243
> >   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:865
> >   do_group_exit+0x177/0x440 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+0x1b9/0x820 arch/x86/entry/common.c:290
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x43f358
> > Code: Bad RIP value.
> > RSP: 002b:00007fff51750198 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:ffffea0006b90c00 count:0 mapcount:-128 mapping:0000000000000000
> > index:0x0
> > flags: 0x2fffc0000000000()
> > raw: 02fffc0000000000 ffffea0006b96408 ffff88021fffac18 0000000000000000
> > raw: 0000000000000000 0000000000000003 00000000ffffff7f 0000000000000000
> > page dumped because: kasan: bad access detected
> > 
> > Memory state around the buggy address:
> >   ffff8801ae42ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >   ffff8801ae42ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > > ffff8801ae430000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> >                     ^
> >   ffff8801ae430080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> >   ffff8801ae430100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > ==================================================================
> > 
> > 
> > ---
> > 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@xxxxxxxxxxxxxxxxx
> > 
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> 

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