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Message-ID: <20240823082522.GS2164@kernel.org>
Date: Fri, 23 Aug 2024 09:25:22 +0100
From: Simon Horman <horms@...nel.org>
To: John Fastabend <john.fastabend@...il.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
syzbot+58c03971700330ce14d8@...kaller.appspotmail.com,
Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf] tcp_bpf: fix return value of tcp_bpf_sendmsg()
On Thu, Aug 22, 2024 at 01:45:51PM -0700, John Fastabend wrote:
> Cong Wang wrote:
> > On Wed, Aug 21, 2024 at 03:55:33PM +0100, Simon Horman wrote:
> > > On Tue, Aug 20, 2024 at 08:07:44PM -0700, Cong Wang wrote:
> > > > From: Cong Wang <cong.wang@...edance.com>
> > > >
> > > > When we cork messages in psock->cork, the last message triggers the
> > > > flushing will result in sending a sk_msg larger than the current
> > > > message size. In this case, in tcp_bpf_send_verdict(), 'copied' becomes
> > > > negative at least in the following case:
> > > >
> > > > 468 case __SK_DROP:
> > > > 469 default:
> > > > 470 sk_msg_free_partial(sk, msg, tosend);
> > > > 471 sk_msg_apply_bytes(psock, tosend);
> > > > 472 *copied -= (tosend + delta); // <==== HERE
> > > > 473 return -EACCES;
> > > >
> > > > Therefore, it could lead to the following BUG with a proper value of
> > > > 'copied' (thanks to syzbot). We should not use negative 'copied' as a
> > > > return value here.
> > > >
> > > > ------------[ cut here ]------------
> > > > kernel BUG at net/socket.c:733!
> > > > Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
> > > > Modules linked in:
> > > > CPU: 0 UID: 0 PID: 3265 Comm: syz-executor510 Not tainted 6.11.0-rc3-syzkaller-00060-gd07b43284ab3 #0
> > > > Hardware name: linux,dummy-virt (DT)
> > > > pstate: 61400009 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> > > > pc : sock_sendmsg_nosec net/socket.c:733 [inline]
> > > > pc : sock_sendmsg_nosec net/socket.c:728 [inline]
> > > > pc : __sock_sendmsg+0x5c/0x60 net/socket.c:745
> > > > lr : sock_sendmsg_nosec net/socket.c:730 [inline]
> > > > lr : __sock_sendmsg+0x54/0x60 net/socket.c:745
> > > > sp : ffff800088ea3b30
> > > > x29: ffff800088ea3b30 x28: fbf00000062bc900 x27: 0000000000000000
> > > > x26: ffff800088ea3bc0 x25: ffff800088ea3bc0 x24: 0000000000000000
> > > > x23: f9f00000048dc000 x22: 0000000000000000 x21: ffff800088ea3d90
> > > > x20: f9f00000048dc000 x19: ffff800088ea3d90 x18: 0000000000000001
> > > > x17: 0000000000000000 x16: 0000000000000000 x15: 000000002002ffaf
> > > > x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
> > > > x11: 0000000000000000 x10: ffff8000815849c0 x9 : ffff8000815b49c0
> > > > x8 : 0000000000000000 x7 : 000000000000003f x6 : 0000000000000000
> > > > x5 : 00000000000007e0 x4 : fff07ffffd239000 x3 : fbf00000062bc900
> > > > x2 : 0000000000000000 x1 : 0000000000000000 x0 : 00000000fffffdef
> > > > Call trace:
> > > > sock_sendmsg_nosec net/socket.c:733 [inline]
> > > > __sock_sendmsg+0x5c/0x60 net/socket.c:745
> > > > ____sys_sendmsg+0x274/0x2ac net/socket.c:2597
> > > > ___sys_sendmsg+0xac/0x100 net/socket.c:2651
> > > > __sys_sendmsg+0x84/0xe0 net/socket.c:2680
> > > > __do_sys_sendmsg net/socket.c:2689 [inline]
> > > > __se_sys_sendmsg net/socket.c:2687 [inline]
> > > > __arm64_sys_sendmsg+0x24/0x30 net/socket.c:2687
> > > > __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
> > > > invoke_syscall+0x48/0x110 arch/arm64/kernel/syscall.c:49
> > > > el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:132
> > > > do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:151
> > > > el0_svc+0x34/0xec arch/arm64/kernel/entry-common.c:712
> > > > el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:730
> > > > el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:598
> > > > Code: f9404463 d63f0060 3108441f 54fffe81 (d4210000)
> > > > ---[ end trace 0000000000000000 ]---
> > > >
> > > > Fixes: 4f738adba30a ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data")
> > > > Reported-by: syzbot+58c03971700330ce14d8@...kaller.appspotmail.com
> > > > Cc: John Fastabend <john.fastabend@...il.com>
> > > > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > > > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > > > ---
> > > > net/ipv4/tcp_bpf.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> > > > index 53b0d62fd2c2..fe6178715ba0 100644
> > > > --- a/net/ipv4/tcp_bpf.c
> > > > +++ b/net/ipv4/tcp_bpf.c
> > > > @@ -577,7 +577,7 @@ static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> > > > err = sk_stream_error(sk, msg->msg_flags, err);
> > > > release_sock(sk);
> > > > sk_psock_put(sk, psock);
> > > > - return copied ? copied : err;
> > > > + return copied > 0 ? copied : err;
> > >
> > > Does it make more sense to make the condition err:
> > > is err 0 iif everything is ok? (completely untested!)
> >
> > Mind to elaborate?
I was thinking that a valid test for for being in an error state is that
err is non-zero. Although given the below, it seems that I was mistaken.
> >
> > From my point of view, 'copied' is to handle partial transmission, for
> > example:
> >
> > 0. User wants to send 2 * 1K bytes with sendmsg()
> > 1. Kernel already sent the first 1K successfully
> > 2. Kernel got some error when sending the 2nd 1K
> >
> > In this scenario, we should return 1K instead of the error to the caller to
> > indicate this partial transmission situation, otherwise we could not
> > distinguish it with a compete failure (that is, 0 byte sent).
>
> Yep, if we don't return the positive value on partial send we will confuse
> apps and they will probably resent data.
>
> >From my side this looks good.
>
> Reviewed-by: John Fastabend <john.fastabend@...il.com>
Thanks for responding to my query.
FWIIW, I am now happy with this patch.
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