linux-kernel - [PATCH] net: initialize local variables in net/ipv6/mcast.c and net/ipv4/igmp.c

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Date:   Fri,  2 Apr 2021 18:36:17 +0100
From:   Phillip Potter <phil@...lpotter.co.uk>
To:     davem@...emloft.net
Cc:     yoshfuji@...ux-ipv6.org, dsahern@...nel.org, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] net: initialize local variables in net/ipv6/mcast.c and net/ipv4/igmp.c

Use memset to initialize two local buffers in net/ipv6/mcast.c,
and another in net/ipv4/igmp.c. Fixes a KMSAN found uninit-value
bug reported by syzbot at:
https://syzkaller.appspot.com/bug?id=0766d38c656abeace60621896d705743aeefed51

Reported-by: syzbot+001516d86dbe88862cec@...kaller.appspotmail.com
Signed-off-by: Phillip Potter <phil@...lpotter.co.uk>
---
 net/ipv4/igmp.c  | 2 ++
 net/ipv6/mcast.c | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 7b272bbed2b4..bc8e358a9a2a 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1131,6 +1131,8 @@ static void ip_mc_filter_add(struct in_device *in_dev, __be32 addr)
 	char buf[MAX_ADDR_LEN];
 	struct net_device *dev = in_dev->dev;
 
+	memset(buf, 0, sizeof(buf));
+
 	/* Checking for IFF_MULTICAST here is WRONG-WRONG-WRONG.
 	   We will get multicast token leakage, when IFF_MULTICAST
 	   is changed. This check should be done in ndo_set_rx_mode
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 6c8604390266..ad90dc28f318 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -658,6 +658,8 @@ static void igmp6_group_added(struct ifmcaddr6 *mc)
 	struct net_device *dev = mc->idev->dev;
 	char buf[MAX_ADDR_LEN];
 
+	memset(buf, 0, sizeof(buf));
+
 	if (IPV6_ADDR_MC_SCOPE(&mc->mca_addr) <
 	    IPV6_ADDR_SCOPE_LINKLOCAL)
 		return;
@@ -694,6 +696,8 @@ static void igmp6_group_dropped(struct ifmcaddr6 *mc)
 	struct net_device *dev = mc->idev->dev;
 	char buf[MAX_ADDR_LEN];
 
+	memset(buf, 0, sizeof(buf));
+
 	if (IPV6_ADDR_MC_SCOPE(&mc->mca_addr) <
 	    IPV6_ADDR_SCOPE_LINKLOCAL)
 		return;
-- 
2.30.2