Re: [PATCH v1] ipv4: add iPv4_is_multicast() check in ip_mc_leave_group().

On 19/01/2021 06:39, Jakub Kicinski wrote:

On Sun, 17 Jan 2021 05:34:16 -0800 wangyingjie55@126.com wrote:

quoted

From: Yingjie Wang <redacted>

There is no iPv4_is_multicast() check added to ip_mc_leave_group()
to check if imr->imr_multiaddr.s_addr is a multicast address.
If not a multicast address, it may result in an error.

Could you please say more? From looking at the code it seems like
no address should match if group is non-mcast, and -EADDRNOTAVAIL 
will be returned.

Adding Nik to CC.

Thanks, and absolutely right. I don't see any point in changing the code, also
you are definitely not fixing any bug. 

quoted

In some cases, the callers of ip_mc_leave_group() don't check
whether it is multicast address or not before calling
such as do_ip_setsockopt(). So I suggest adding the ipv4_is_multicast()
check to the ip_mc_leave_group() to prevent this from happening.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yingjie Wang <redacted>
---
 net/ipv4/igmp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 7b272bbed2b4..1b6f91271cfd 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c

@@ -2248,6 +2248,9 @@ int ip_mc_leave_group(struct sock *sk, struct ip_mreqn *imr)
 	u32 ifindex;
 	int ret = -EADDRNOTAVAIL;
 
+	if (!ipv4_is_multicast(group))
+		return -EINVAL;
+
 	ASSERT_RTNL();
 
 	in_dev = ip_mc_find_dev(net, imr);