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Date:   Fri, 03 Mar 2017 06:32:56 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Gerrit Renker <gerrit@....abdn.ac.uk>,
        "David S. Miller" <davem@...emloft.net>, dccp@...r.kernel.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: net/dccp: use-after-free in dccp_feat_activate_values

On Fri, 2017-03-03 at 15:11 +0100, Dmitry Vyukov wrote:
> On Mon, Feb 13, 2017 at 11:29 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Mon, Feb 13, 2017 at 11:19 AM, Andrey Konovalov
> > <andreyknvl@...gle.com> wrote:
> >> Hi,
> >>
> >> I've got the following error report while fuzzing the kernel with syzkaller.
> >>
> >> On commit 926af6273fc683cd98cd0ce7bf0d04a02eed6742.
> >>
> >> A reproducer and .config are attached.
> >> Note, that it takes quite some time to trigger the bug (up to 10 minutes).
> >>
> >> BUG: KASAN: use-after-free in dccp_feat_activate_values+0x967/0xab0
> >> net/dccp/feat.c:1541 at addr ffff88003713be68
> >> Read of size 8 by task syz-executor2/8457
> >> CPU: 2 PID: 8457 Comm: syz-executor2 Not tainted 4.10.0-rc7+ #127
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> Call Trace:
> >>  <IRQ>
> >>  __dump_stack lib/dump_stack.c:15 [inline]
> >>  dump_stack+0x292/0x398 lib/dump_stack.c:51
> >>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:162
> >>  print_address_description mm/kasan/report.c:200 [inline]
> >>  kasan_report_error mm/kasan/report.c:289 [inline]
> >>  kasan_report.part.1+0x20e/0x4e0 mm/kasan/report.c:311
> >>  kasan_report mm/kasan/report.c:332 [inline]
> >>  __asan_report_load8_noabort+0x29/0x30 mm/kasan/report.c:332
> >>  dccp_feat_activate_values+0x967/0xab0 net/dccp/feat.c:1541
> >>  dccp_create_openreq_child+0x464/0x610 net/dccp/minisocks.c:121
> >>  dccp_v6_request_recv_sock+0x1f6/0x1960 net/dccp/ipv6.c:457
> >>  dccp_check_req+0x335/0x5a0 net/dccp/minisocks.c:186
> >>  dccp_v6_rcv+0x69e/0x1d00 net/dccp/ipv6.c:711
> >>  ip6_input_finish+0x46d/0x17a0 net/ipv6/ip6_input.c:279
> >>  NF_HOOK include/linux/netfilter.h:257 [inline]
> >>  ip6_input+0xdb/0x590 net/ipv6/ip6_input.c:322
> >>  dst_input include/net/dst.h:507 [inline]
> >>  ip6_rcv_finish+0x289/0x890 net/ipv6/ip6_input.c:69
> >>  NF_HOOK include/linux/netfilter.h:257 [inline]
> >>  ipv6_rcv+0x12ec/0x23d0 net/ipv6/ip6_input.c:203
> >>  __netif_receive_skb_core+0x1ae5/0x3400 net/core/dev.c:4190
> >>  __netif_receive_skb+0x2a/0x170 net/core/dev.c:4228
> >>  process_backlog+0xe5/0x6c0 net/core/dev.c:4839
> >>  napi_poll net/core/dev.c:5202 [inline]
> >>  net_rx_action+0xe70/0x1900 net/core/dev.c:5267
> >>  __do_softirq+0x2fb/0xb7d kernel/softirq.c:284
> >>  do_softirq_own_stack+0x1c/0x30 arch/x86/entry/entry_64.S:902
> >
> >
> > Seems there is a race condition between iterating dccp_feat_entry
> > and freeing it, bh_lock_sock() seems not held in this path.
> 
> 
> 
> Cong, where exactly do we need to add bh_lock_sock()?
> 
> I am still seeing this on 4977ab6e92e267afe9d8f78438c3db330ca8434c


I would try :

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 409d0cfd34474812c3bf74f26cd423a3d65ee441..5a8b5ac5edaaf35428ab04cc810d98310bd169ed 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -482,7 +482,9 @@ static int dccp_v4_send_response(const struct sock *sk, struct request_sock *req
 	if (dst == NULL)
 		goto out;
 
+	bh_lock_sock(sk);
 	skb = dccp_make_response(sk, dst, req);
+	bh_unlock_sock(sk);
 	if (skb != NULL) {
 		const struct inet_request_sock *ireq = inet_rsk(req);
 		struct dccp_hdr *dh = dccp_hdr(skb);
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 233b57367758c64c09ed40f7359cb8fcb1918d93..e89cc88d14c22d411a91afab093e209fcbb816d8 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -214,7 +214,9 @@ static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req
 		goto done;
 	}
 
+	bh_lock_sock(sk);
 	skb = dccp_make_response(sk, dst, req);
+	bh_unlock_sock(sk);
 	if (skb != NULL) {
 		struct dccp_hdr *dh = dccp_hdr(skb);
 		struct ipv6_txoptions *opt;


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