* Re: general protection fault in selinux_socket_recvmsg
2020-05-23 7:14 general protection fault in selinux_socket_recvmsg syzbot
@ 2020-05-23 12:16 ` Ondrej Mosnacek
2020-05-24 18:12 ` syzbot
1 sibling, 0 replies; 3+ messages in thread
From: Ondrej Mosnacek @ 2020-05-23 12:16 UTC (permalink / raw)
To: syzbot
Cc: andriin, anton, ast, bpf, ccross, daniel, Eric Paris,
john.fastabend, kafai, Kees Cook, kpsingh,
Linux kernel mailing list, network dev, Paul Moore, SElinux list,
songliubraving, Stephen Smalley, syzkaller-bugs, tony.luck, yhs,
Mat Martineau, Matthieu Baerts, mptcp, Paolo Abeni
On Sat, May 23, 2020 at 9:14 AM syzbot
<syzbot+c6bfc3db991edc918432@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 051143e1 Merge tag 'apparmor-pr-2020-05-21' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1313f016100000
> kernel config: https://syzkaller.appspot.com/x/.config?x=b3368ce0cc5f5ace
> dashboard link: https://syzkaller.appspot.com/bug?extid=c6bfc3db991edc918432
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13eeacba100000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167163e6100000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+c6bfc3db991edc918432@syzkaller.appspotmail.com
>
> general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
> CPU: 0 PID: 7370 Comm: syz-executor283 Not tainted 5.7.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:selinux_socket_recvmsg+0x1e/0x40 security/selinux/hooks.c:4841
OK, this is obviously not a SELinux bug - the hook just gets sock ==
NULL from the net stack, which is just plain wrong...
> Code: e8 77 f9 1e fe 48 89 ef 5d eb b1 90 53 48 89 fb e8 67 f9 1e fe 48 8d 7b 18 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0f 48 8b 7b 18 be 02 00 00 00 5b e9 7d fc ff ff e8
> RSP: 0018:ffffc900019d7a58 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000040000000
> RDX: 0000000000000003 RSI: ffffffff83543bb9 RDI: 0000000000000018
> RBP: dffffc0000000000 R08: ffff88809f45a180 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
> R13: ffffc900019d7d78 R14: 0000000000001000 R15: 0000000040000000
> FS: 00007f5ffb311700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f5ffb2efe78 CR3: 00000000a33c1000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> security_socket_recvmsg+0x78/0xc0 security/security.c:2070
> sock_recvmsg+0x47/0x110 net/socket.c:902
> mptcp_recvmsg+0xb3b/0xd90 net/mptcp/protocol.c:891
...but this function looks suspicious. If the "unlikely(ssock)" check
at [1] fails, then we continue in the rest of the function with ssock
== NULL. However, when the "unlikely(__mptcp_tcp_fallback(msk))" check
at [2] succeeds, we jump to the "fallback" label, where it is assumed
that ssock != NULL. That seems like an obvious bug to me and I bet
that's what causes the crash.
If I understand the code correctly, the fix should be just to change
this at [2]:
- if (unlikely(__mptcp_tcp_fallback(msk)))
+ if (unlikely(ssock = __mptcp_tcp_fallback(msk)))
@MPTCP folks, can you have a look?
[1] https://elixir.bootlin.com/linux/v5.7-rc6/source/net/mptcp/protocol.c#L886
[2] https://elixir.bootlin.com/linux/v5.7-rc6/source/net/mptcp/protocol.c#L957
> inet_recvmsg+0x121/0x5d0 net/ipv4/af_inet.c:838
> sock_recvmsg_nosec net/socket.c:886 [inline]
> sock_recvmsg net/socket.c:904 [inline]
> sock_recvmsg+0xca/0x110 net/socket.c:900
> __sys_recvfrom+0x1c5/0x2f0 net/socket.c:2057
> __do_sys_recvfrom net/socket.c:2075 [inline]
> __se_sys_recvfrom net/socket.c:2071 [inline]
> __x64_sys_recvfrom+0xdd/0x1b0 net/socket.c:2071
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x448ef9
> Code: e8 cc 14 03 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 9b 0c fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f5ffb310da8 EFLAGS: 00000246 ORIG_RAX: 000000000000002d
> RAX: ffffffffffffffda RBX: 00000000006dec28 RCX: 0000000000448ef9
> RDX: 0000000000001000 RSI: 00000000200004c0 RDI: 0000000000000003
> RBP: 00000000006dec20 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000040000000 R11: 0000000000000246 R12: 00000000006dec2c
> R13: 00007ffc3a001ccf R14: 00007f5ffb3119c0 R15: 00000000006dec2c
> Modules linked in:
> ---[ end trace 60e1f3eb5a5b83ce ]---
> RIP: 0010:selinux_socket_recvmsg+0x1e/0x40 security/selinux/hooks.c:4841
> Code: e8 77 f9 1e fe 48 89 ef 5d eb b1 90 53 48 89 fb e8 67 f9 1e fe 48 8d 7b 18 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0f 48 8b 7b 18 be 02 00 00 00 5b e9 7d fc ff ff e8
> RSP: 0018:ffffc900019d7a58 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000040000000
> RDX: 0000000000000003 RSI: ffffffff83543bb9 RDI: 0000000000000018
> RBP: dffffc0000000000 R08: ffff88809f45a180 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
> R13: ffffc900019d7d78 R14: 0000000000001000 R15: 0000000040000000
> FS: 00007f5ffb311700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f5ffb2efe78 CR3: 00000000a33c1000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
> 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@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
--
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: general protection fault in selinux_socket_recvmsg
2020-05-23 7:14 general protection fault in selinux_socket_recvmsg syzbot
2020-05-23 12:16 ` Ondrej Mosnacek
@ 2020-05-24 18:12 ` syzbot
1 sibling, 0 replies; 3+ messages in thread
From: syzbot @ 2020-05-24 18:12 UTC (permalink / raw)
To: andriin, anton, ast, bpf, ccross, daniel, davem, dvyukov,
edumazet, eparis, john.fastabend, kafai, keescook, kpsingh, kuba,
kuznet, linux-kernel, mathew.j.martineau, matthieu.baerts, mptcp,
netdev, omosnace, pabeni, paul, penguin-kernel, selinux,
songliubraving, stephen.smalley.work, syzkaller-bugs, tony.luck,
yhs, yoshfuji
syzbot has bisected this bug to:
commit 263e1201a2c324b60b15ecda5de9ebf1e7293e31
Author: Paolo Abeni <pabeni@redhat.com>
Date: Thu Apr 30 13:01:51 2020 +0000
mptcp: consolidate synack processing.
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12a5254a100000
start commit: 051143e1 Merge tag 'apparmor-pr-2020-05-21' of git://git.k..
git tree: upstream
final crash: https://syzkaller.appspot.com/x/report.txt?x=11a5254a100000
console output: https://syzkaller.appspot.com/x/log.txt?x=16a5254a100000
kernel config: https://syzkaller.appspot.com/x/.config?x=b3368ce0cc5f5ace
dashboard link: https://syzkaller.appspot.com/bug?extid=c6bfc3db991edc918432
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13eeacba100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167163e6100000
Reported-by: syzbot+c6bfc3db991edc918432@syzkaller.appspotmail.com
Fixes: 263e1201a2c3 ("mptcp: consolidate synack processing.")
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
^ permalink raw reply [flat|nested] 3+ messages in thread