ipv6: take rcu lock in rawv6_send_hdrinc()

tracywwnj · bwhacks · commit 9db8f411f90e · 2018-12-16T22:09:36.000Z
commit a688caa upstream. In rawv6_send_hdrinc(), in order to avoid an extra dst_hold(), we directly assign the dst to skb and set passed in dst to NULL to avoid double free. However, in error case, we free skb and then do stats update with the dst pointer passed in. This causes use-after-free on the dst. Fix it by taking rcu read lock right before dst could get released to make sure dst does not get freed until the stats update is done. Note: we don't have this issue in ipv4 cause dst is not used for stats update in v4. Syzkaller reported following crash: BUG: KASAN: use-after-free in rawv6_send_hdrinc net/ipv6/raw.c:692 [inline] BUG: KASAN: use-after-free in rawv6_sendmsg+0x4421/0x4630 net/ipv6/raw.c:921 Read of size 8 at addr ffff8801d95ba730 by task syz-executor0/32088 CPU: 1 PID: 32088 Comm: syz-executor0 Not tainted 4.19.0-rc2+ #93 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 rawv6_send_hdrinc net/ipv6/raw.c:692 [inline] rawv6_sendmsg+0x4421/0x4630 net/ipv6/raw.c:921 inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798 sock_sendmsg_nosec net/socket.c:621 [inline] sock_sendmsg+0xd5/0x120 net/socket.c:631 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2114 __sys_sendmsg+0x11d/0x280 net/socket.c:2152 __do_sys_sendmsg net/socket.c:2161 [inline] __se_sys_sendmsg net/socket.c:2159 [inline] __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2159 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457099 Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f83756edc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f83756ee6d4 RCX: 0000000000457099 RDX: 0000000000000000 RSI: 0000000020003840 RDI: 0000000000000004 RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00000000004d4b30 R14: 00000000004c90b1 R15: 0000000000000000 Allocated by task 32088: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490 kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554 dst_alloc+0xbb/0x1d0 net/core/dst.c:105 ip6_dst_alloc+0x35/0xa0 net/ipv6/route.c:353 ip6_rt_cache_alloc+0x247/0x7b0 net/ipv6/route.c:1186 ip6_pol_route+0x8f8/0xd90 net/ipv6/route.c:1895 ip6_pol_route_output+0x54/0x70 net/ipv6/route.c:2093 fib6_rule_lookup+0x277/0x860 net/ipv6/fib6_rules.c:122 ip6_route_output_flags+0x2c5/0x350 net/ipv6/route.c:2121 ip6_route_output include/net/ip6_route.h:88 [inline] ip6_dst_lookup_tail+0xe27/0x1d60 net/ipv6/ip6_output.c:951 ip6_dst_lookup_flow+0xc8/0x270 net/ipv6/ip6_output.c:1079 rawv6_sendmsg+0x12d9/0x4630 net/ipv6/raw.c:905 inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798 sock_sendmsg_nosec net/socket.c:621 [inline] sock_sendmsg+0xd5/0x120 net/socket.c:631 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2114 __sys_sendmsg+0x11d/0x280 net/socket.c:2152 __do_sys_sendmsg net/socket.c:2161 [inline] __se_sys_sendmsg net/socket.c:2159 [inline] __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2159 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 5356: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3498 [inline] kmem_cache_free+0x83/0x290 mm/slab.c:3756 dst_destroy+0x267/0x3c0 net/core/dst.c:141 dst_destroy_rcu+0x16/0x19 net/core/dst.c:154 __rcu_reclaim kernel/rcu/rcu.h:236 [inline] rcu_do_batch kernel/rcu/tree.c:2576 [inline] invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline] __rcu_process_callbacks kernel/rcu/tree.c:2847 [inline] rcu_process_callbacks+0xf23/0x2670 kernel/rcu/tree.c:2864 __do_softirq+0x30b/0xad8 kernel/softirq.c:292 Fixes: 1789a64 ("raw: avoid two atomics in xmit") Signed-off-by: Wei Wang <weiwan@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> [bwh: Backported to 3.16: - We don't set tstamp here - Adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
@@ -643,8 +643,6 @@ static int rawv6_send_hdrinc(struct sock *sk, void *from, int length,
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
-	skb_dst_set(skb, &rt->dst);
-	*dstp = NULL;
 
 	skb_put(skb, length);
 	skb_reset_network_header(skb);
@@ -654,24 +652,37 @@ static int rawv6_send_hdrinc(struct sock *sk, void *from, int length,
 
 	skb->transport_header = skb->network_header;
 	err = memcpy_fromiovecend((void *)iph, from, 0, length);
-	if (err)
-		goto error_fault;
+	if (err) {
+		err = -EFAULT;
+		kfree_skb(skb);
+		goto error;
+	}
 
+	skb_dst_set(skb, &rt->dst);
+	*dstp = NULL;
+
+	/* Acquire rcu_read_lock() in case we need to use rt->rt6i_idev
+	 * in the error path. Since skb has been freed, the dst could
+	 * have been queued for deletion.
+	 */
+	rcu_read_lock();
 	IP6_UPD_PO_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUT, skb->len);
 	err = NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, skb, NULL,
 		      rt->dst.dev, dst_output);
 	if (err > 0)
 		err = net_xmit_errno(err);
-	if (err)
-		goto error;
+	if (err) {
+		IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
+		rcu_read_unlock();
+		goto error_check;
+	}
+	rcu_read_unlock();
 out:
 	return 0;
 
-error_fault:
-	err = -EFAULT;
-	kfree_skb(skb);
 error:
 	IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
+error_check:
 	if (err == -ENOBUFS && !np->recverr)
 		err = 0;
 	return err;
