Re: net/dccp: use-after-free in dccp_feat_activate_values

[Eric Dumazet]

On Fri, 2017-03-03 at 06:32 -0800, Eric Dumazet wrote:
> 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@xxxxxxxxx> wrote:
> > > On Mon, Feb 13, 2017 at 11:19 AM, Andrey Konovalov
> > > <andreyknvl@xxxxxxxxxx> 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 :

Or something that would compile. I will take a deeper look after my
commute.

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 409d0cfd34474812c3bf74f26cd423a3d65ee441..56f883b301ccd610fc24efeac4fb47d3c2f95ecf 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -482,7 +482,11 @@ static int dccp_v4_send_response(const struct sock *sk, struct request_sock *req
 	if (dst == NULL)
 		goto out;
 
+	/* DCCP is not ready yet for lockless SYN processing */
+	bh_lock_sock((struct sock *)sk);
 	skb = dccp_make_response(sk, dst, req);
+	bh_unlock_sock((struct 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..673f45f85b7c755c8165c6274ffb6b1fe5660683 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -214,7 +214,11 @@ static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req
 		goto done;
 	}
 
+	/* DCCP is not ready yet for lockless SYN processing */
+	bh_lock_sock((struct sock *)sk);
 	skb = dccp_make_response(sk, dst, req);
+	bh_unlock_sock((struct sock *)sk);
+
 	if (skb != NULL) {
 		struct dccp_hdr *dh = dccp_hdr(skb);
 		struct ipv6_txoptions *opt;