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Date:   Tue, 21 Jul 2020 19:22:36 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Tuong Lien <tuong.t.lien@...tech.com.au>
Cc:     davem <davem@...emloft.net>, jmaloy@...hat.com, maloy@...jonn.com,
        Ying Xue <ying.xue@...driver.com>,
        network dev <netdev@...r.kernel.org>,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [tipc-discussion] [net-next] tipc: fix NULL pointer dereference
 in streaming

On Wed, Jun 3, 2020 at 1:06 PM Tuong Lien <tuong.t.lien@...tech.com.au> wrote:
>
> syzbot found the following crash:
>
> general protection fault, probably for non-canonical address 0xdffffc0000000019: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x00000000000000c8-0x00000000000000cf]
> CPU: 1 PID: 7060 Comm: syz-executor394 Not tainted 5.7.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__tipc_sendstream+0xbde/0x11f0 net/tipc/socket.c:1591
> Code: 00 00 00 00 48 39 5c 24 28 48 0f 44 d8 e8 fa 3e db f9 48 b8 00 00 00 00 00 fc ff df 48 8d bb c8 00 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 e2 04 00 00 48 8b 9b c8 00 00 00 48 b8 00 00 00
> RSP: 0018:ffffc90003ef7818 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff8797fd9d
> RDX: 0000000000000019 RSI: ffffffff8797fde6 RDI: 00000000000000c8
> RBP: ffff888099848040 R08: ffff88809a5f6440 R09: fffffbfff1860b4c
> R10: ffffffff8c305a5f R11: fffffbfff1860b4b R12: ffff88809984857e
> R13: 0000000000000000 R14: ffff888086aa4000 R15: 0000000000000000
> FS:  00000000009b4880(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000140 CR3: 00000000a7fdf000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  tipc_sendstream+0x4c/0x70 net/tipc/socket.c:1533
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x32f/0x810 net/socket.c:2352
>  ___sys_sendmsg+0x100/0x170 net/socket.c:2406
>  __sys_sendmmsg+0x195/0x480 net/socket.c:2496
>  __do_sys_sendmmsg net/socket.c:2525 [inline]
>  __se_sys_sendmmsg net/socket.c:2522 [inline]
>  __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2522
>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x440199
> ...
>
> This bug was bisected to commit 0a3e060f340d ("tipc: add test for Nagle
> algorithm effectiveness"). However, it is not the case, the trouble was
> from the base in the case of zero data length message sending, we would
> unexpectedly make an empty 'txq' queue after the 'tipc_msg_append()' in
> Nagle mode.
>
> A similar crash can be generated even without the bisected patch but at
> the link layer when it accesses the empty queue.
>
> We solve the issues by building at least one buffer to go with socket's
> header and an optional data section that may be empty like what we had
> with the 'tipc_msg_build()'.
>
> Note: the previous commit 4c21daae3dbc ("tipc: Fix NULL pointer
> dereference in __tipc_sendstream()") is obsoleted by this one since the
> 'txq' will be never empty and the check of 'skb != NULL' is unnecessary
> but it is safe anyway.
Hi, Tuong

If commit 4c21daae3dbc is obsoleted by this one, can you please
send a patch to revert it?

Thanks.

>
> Reported-by: syzbot+8eac6d030e7807c21d32@...kaller.appspotmail.com
> Fixes: c0bceb97db9e ("tipc: add smart nagle feature")
> Acked-by: Jon Maloy <jmaloy@...hat.com>
> Signed-off-by: Tuong Lien <tuong.t.lien@...tech.com.au>
> ---
>  net/tipc/msg.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/tipc/msg.c b/net/tipc/msg.c
> index c0afcd627c5e..046e4cb3acea 100644
> --- a/net/tipc/msg.c
> +++ b/net/tipc/msg.c
> @@ -221,7 +221,7 @@ int tipc_msg_append(struct tipc_msg *_hdr, struct msghdr *m, int dlen,
>         accounted = skb ? msg_blocks(buf_msg(skb)) : 0;
>         total = accounted;
>
> -       while (rem) {
> +       do {
>                 if (!skb || skb->len >= mss) {
>                         skb = tipc_buf_acquire(mss, GFP_KERNEL);
>                         if (unlikely(!skb))
> @@ -245,7 +245,7 @@ int tipc_msg_append(struct tipc_msg *_hdr, struct msghdr *m, int dlen,
>                 skb_put(skb, cpy);
>                 rem -= cpy;
>                 total += msg_blocks(hdr) - curr;
> -       }
> +       } while (rem);
>         return total - accounted;
>  }
>
> --
> 2.13.7
>
>
>
> _______________________________________________
> tipc-discussion mailing list
> tipc-discussion@...ts.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/tipc-discussion

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