On Mon, Feb 24, 2020 at 11:47 PM Paul Moore [off-list ref] wrote:

On Mon, Feb 24, 2020 at 5:43 PM Eric Paris [off-list ref] wrote:

quoted

https://syzkaller.appspot.com/x/repro.syz?x=151b1109e00000 (the
reproducer listed) looks like it is literally fuzzing the AUDIT_SET.
Which seems like this is working as designed if it is setting the
failure mode to 2.

So it is, good catch :)  I saw the panic and instinctively chalked
that up to a mistaken config, not expecting that it was what was being
tested.

Yes, this audit failure mode is quite unpleasant for fuzzing. And
since this is not a top-level syscall argument value, it's effectively
impossible to filter out in the fuzzer. Maybe another use case for the
"fuzer lockdown" feature +Tetsuo proposed.
With the current state of the things, I think we only have an option
to disable fuzzing of audit. Which is pity because it has found 5 or
so real bugs in audit too.
But this happened anyway because audit is only reachable from init pid
namespace and syzkaller always unshares pid namespace for sandboxing
reasons, that was removed accidentally and that's how it managed to
find the bugs. But the unshare is restored now:
https://github.com/google/syzkaller/commit/5e0e1d1450d7c3497338082fc28912fdd7f93a3c

As a side effect all other real bugs in audit will be auto-obsoleted
in future if not fixed because they will stop happening.

#syz invalid

quoted

On Mon, 2020-02-24 at 17:38 -0500, Paul Moore wrote:

quoted

On Mon, Feb 24, 2020 at 3:18 AM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following crash on:

HEAD commit:    36a44bcd Merge branch 'bnxt_en-shutdown-and-kexec-
kdump-re..
git tree:       net
console output:
https://syzkaller.appspot.com/x/log.txt?x=148bfdd9e00000
kernel config:
https://syzkaller.appspot.com/x/.config?x=768cc3d3e277cc16
dashboard link:
https://syzkaller.appspot.com/bug?extid=9a5e789e4725b9ef1316
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:
https://syzkaller.appspot.com/x/repro.syz?x=151b1109e00000
C reproducer:
https://syzkaller.appspot.com/x/repro.c?x=128bfdd9e00000

The bug was bisected to:

commit 0c1b9970ddd4cc41002321c3877e7f91aacb896d
Author: Dan Carpenter [off-list ref]
Date:   Fri Jul 28 14:42:27 2017 +0000

    staging: lustre: lustre: Off by two in lmv_fid2path()

bisection log:
https://syzkaller.appspot.com/x/bisect.txt?x=17e6c3e9e00000
final crash:
https://syzkaller.appspot.com/x/report.txt?x=1416c3e9e00000
console output:
https://syzkaller.appspot.com/x/log.txt?x=1016c3e9e00000

IMPORTANT: if you fix the bug, please add the following tag to the
commit:
Reported-by: syzbot+9a5e789e4725b9ef1316@syzkaller.appspotmail.com
Fixes: 0c1b9970ddd4 ("staging: lustre: lustre: Off by two in
lmv_fid2path()")

audit: audit_backlog=13 > audit_backlog_limit=7
audit: audit_lost=1 audit_rate_limit=0 audit_backlog_limit=7
Kernel panic - not syncing: audit: backlog limit exceeded
CPU: 1 PID: 9913 Comm: syz-executor024 Not tainted 5.6.0-rc1-
syzkaller #0
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+0x197/0x210 lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:221
 audit_panic.cold+0x32/0x32 kernel/audit.c:307
 audit_log_lost kernel/audit.c:377 [inline]
 audit_log_lost+0x8b/0x180 kernel/audit.c:349
 audit_log_start kernel/audit.c:1788 [inline]
 audit_log_start+0x70e/0x7c0 kernel/audit.c:1745
 audit_log+0x95/0x120 kernel/audit.c:2345
 xt_replace_table+0x61d/0x830 net/netfilter/x_tables.c:1413
 __do_replace+0x1da/0x950 net/ipv6/netfilter/ip6_tables.c:1084
 do_replace net/ipv6/netfilter/ip6_tables.c:1157 [inline]
 do_ip6t_set_ctl+0x33a/0x4c8 net/ipv6/netfilter/ip6_tables.c:1681
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x77/0xd0 net/netfilter/nf_sockopt.c:115
 ipv6_setsockopt net/ipv6/ipv6_sockglue.c:949 [inline]
 ipv6_setsockopt+0x147/0x180 net/ipv6/ipv6_sockglue.c:933
 tcp_setsockopt net/ipv4/tcp.c:3165 [inline]
 tcp_setsockopt+0x8f/0xe0 net/ipv4/tcp.c:3159
 sock_common_setsockopt+0x94/0xd0 net/core/sock.c:3149
 __sys_setsockopt+0x261/0x4c0 net/socket.c:2130
 __do_sys_setsockopt net/socket.c:2146 [inline]
 __se_sys_setsockopt net/socket.c:2143 [inline]
 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:2143
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44720a
Code: 49 89 ca b8 37 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 1a e0
fb ff c3 66 0f 1f 84 00 00 00 00 00 49 89 ca b8 36 00 00 00 0f 05
<48> 3d 01 f0 ff ff 0f 83 fa df fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007ffd032dec78 EFLAGS: 00000286 ORIG_RAX:
0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000044720a
RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000003
RBP: 00007ffd032deda0 R08: 00000000000003b8 R09: 0000000000004000
R10: 00000000006d7b40 R11: 0000000000000286 R12: 00007ffd032deca0
R13: 00000000006d9d60 R14: 0000000000000029 R15: 00000000006d7ba0
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
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For information about bisection process see:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Similar to syzbot report 72461ac44b36c98f58e5, see my comments there.