Re: net/sctp: null-ptr-deref in sctp_inet_listen

[Xin Long]

On Tue, Nov 8, 2016 at 5:44 AM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> Hi,
>
> I've got the following error report while running the syzkaller fuzzer:
>
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 1 PID: 3851 Comm: a.out Not tainted 4.9.0-rc4+ #354
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880065f1d800 task.stack: ffff880063840000
> RIP: 0010:[<ffffffff8394151b>]  [<ffffffff8394151b>]
> sctp_inet_listen+0x29b/0x790 net/sctp/socket.c:6870
> RSP: 0018:ffff880063847dd0  EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 1ffff1000c708fbd RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
> RBP: ffff880063847e70 R08: dffffc0000000000 R09: dffffc0000000000
> R10: 0000000000000002 R11: 0000000000000002 R12: ffff88006b350800
> R13: 0000000000000000 R14: 1ffff1000d66a1a5 R15: 0000000000000000
> FS:  00007fd1f0f3d7c0(0000) GS:ffff88006cd00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000000 CR3: 0000000064af9000 CR4: 00000000000006e0
> Stack:
>  ffff880063847de0 ffff880066165900 ffff88006b350d20 0000000041b58ab3
>  ffffffff847ff589 ffffffff83941280 dffffc0000000000 0000000000000000
>  ffff880069b9f740 0000000000000000 ffff880063847e38 ffffffff819f04ef
> Call Trace:
>  [<     inline     >] SYSC_listen net/socket.c:1396
>  [<ffffffff82b73cf6>] SyS_listen+0x206/0x250 net/socket.c:1382
>  [<ffffffff83fc1501>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> arch/x86/entry/entry_64.S:209
> Code: 00 0f 85 f4 04 00 00 4d 8b ac 24 28 05 00 00 49 b8 00 00 00 00
> 00 fc ff df 49 8d 7d 02 48 89 fe 49 89 fa 48 c1 ee 03 41 83 e2 07 <46>
> 0f b6 0c 06 41 83 c2 01 45 38 ca 7c 09 45 84 c9 0f 85 87 04
> RIP  [<ffffffff8394151b>] sctp_inet_listen+0x29b/0x790 net/sctp/socket.c:6870
>  RSP <ffff880063847dd0>
> ---[ end trace f2b501fc22999b37 ]---
>
> A reproducer is attached.
>
> On commit bc33b0ca11e3df467777a4fa7639ba488c9d4911 (Nov 5).
>
This is a shutdown injection issue.
sctp_shutdown need a sk->state check, just like tcp_shutdown:

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4287,7 +4287,8 @@ static void sctp_shutdown(struct sock *sk, int how)
        if (!sctp_style(sk, TCP))
                return;

-       if (how & SEND_SHUTDOWN) {
+       if (how & SEND_SHUTDOWN &&
+           (1 << sk->sk_state) & (SCTP_SS_ESTABLISHED | SCTP_SS_CLOSING)) {
                sk->sk_state = SCTP_SS_CLOSING;
                ep = sctp_sk(sk)->ep;
                if (!list_empty(&ep->asocs)) {