[PATCH net-next] net/ipv6: Fix ip6_convert_metrics() bug

[PATCH net-next] net/ipv6: Fix ip6_convert_metrics() bug

[Eric Dumazet]

If ip6_convert_metrics() fails to allocate memory, it should not
overwrite rt->fib6_metrics or we risk a crash later as syzbot found.

BUG: KASAN: null-ptr-deref in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
BUG: KASAN: null-ptr-deref in refcount_sub_and_test+0x92/0x330 lib/refcount.c:179
Read of size 4 at addr 0000000000000044 by task syzkaller832429/4487

CPU: 1 PID: 4487 Comm: syzkaller832429 Not tainted 4.16.0+ #6
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+0x1b9/0x294 lib/dump_stack.c:113
 kasan_report_error mm/kasan/report.c:352 [inline]
 kasan_report.cold.7+0x6d/0x2fe mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
 atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
 refcount_sub_and_test+0x92/0x330 lib/refcount.c:179
 refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212
 fib6_info_destroy+0x2d0/0x3c0 net/ipv6/ip6_fib.c:206
 fib6_info_release include/net/ip6_fib.h:304 [inline]
 ip6_route_info_create+0x677/0x3240 net/ipv6/route.c:3020
 ip6_route_add+0x23/0xb0 net/ipv6/route.c:3030
 inet6_rtm_newroute+0x142/0x160 net/ipv6/route.c:4406
 rtnetlink_rcv_msg+0x466/0xc10 net/core/rtnetlink.c:4648
 netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2448
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4666
 netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
 netlink_unicast+0x58b/0x740 net/netlink/af_netlink.c:1336
 netlink_sendmsg+0x9f0/0xfa0 net/netlink/af_netlink.c:1901
 sock_sendmsg_nosec net/socket.c:629 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:639
 ___sys_sendmsg+0x805/0x940 net/socket.c:2117
 __sys_sendmsg+0x115/0x270 net/socket.c:2155
 SYSC_sendmsg net/socket.c:2164 [inline]
 SyS_sendmsg+0x29/0x30 net/socket.c:2162
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Ahern <dsa@cumulusnetworks.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/ipv6/route.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f9c363327d620322dda2269d8398a5dc5de7aa4e..9279f4ec84b6b885357390d3de0826a8a4c54daf 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2600,21 +2600,19 @@ static int ip6_dst_gc(struct dst_ops *ops)
 static int ip6_convert_metrics(struct net *net, struct fib6_info *rt,
 			       struct fib6_config *cfg)
 {
-	int err = 0;
+	struct dst_metrics *p;
 
-	if (cfg->fc_mx) {
-		rt->fib6_metrics = kzalloc(sizeof(*rt->fib6_metrics),
-					   GFP_KERNEL);
-		if (unlikely(!rt->fib6_metrics))
-			return -ENOMEM;
+	if (!cfg->fc_mx)
+		return 0;
 
-		refcount_set(&rt->fib6_metrics->refcnt, 1);
+	p = kzalloc(sizeof(*rt->fib6_metrics), GFP_KERNEL);
+	if (unlikely(!p))
+		return -ENOMEM;
 
-		err = ip_metrics_convert(net, cfg->fc_mx, cfg->fc_mx_len,
-					 rt->fib6_metrics->metrics);
-	}
+	refcount_set(&p->refcnt, 1);
+	rt->fib6_metrics = p;
 
-	return err;
+	return ip_metrics_convert(net, cfg->fc_mx, cfg->fc_mx_len, p->metrics);
 }
 
 static struct rt6_info *ip6_nh_lookup_table(struct net *net,
-- 
2.17.0.484.g0c8726318c-goog

Re: [PATCH net-next] net/ipv6: Fix ip6_convert_metrics() bug

[David Ahern]

On 4/19/18 10:14 AM, Eric Dumazet wrote:
> If ip6_convert_metrics() fails to allocate memory, it should not
> overwrite rt->fib6_metrics or we risk a crash later as syzbot found.
> 

...

> 
> Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: David Ahern <dsa@cumulusnetworks.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>
> ---
>  net/ipv6/route.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)

Acked-by: David Ahern <dsa@cumulusnetworks.com>

Thanks for fixing.

Re: [PATCH net-next] net/ipv6: Fix ip6_convert_metrics() bug

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Thu, 19 Apr 2018 09:14:53 -0700

> If ip6_convert_metrics() fails to allocate memory, it should not
> overwrite rt->fib6_metrics or we risk a crash later as syzbot found.
 ...
> Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: David Ahern <dsa@cumulusnetworks.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>

Applied, thanks Eric.