netdev - [PATCH net] icmp: prevent possible NULL dereferences from icmp_build

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Message-ID: <20240419105332.2430179-1-edumazet@google.com>
Date: Fri, 19 Apr 2024 10:53:32 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Andreas Roeseler <andreas.a.roeseler@...il.com>
Subject: [PATCH net] icmp: prevent possible NULL dereferences from icmp_build_probe()

First problem is a double call to __in_dev_get_rcu(), because
the second one could return NULL.

if (__in_dev_get_rcu(dev) && __in_dev_get_rcu(dev)->ifa_list)

Second problem is a read from dev->ip6_ptr with no NULL check:

if (!list_empty(&rcu_dereference(dev->ip6_ptr)->addr_list))

Use the correct RCU API to fix these.

Fixes: d329ea5bd884 ("icmp: add response to RFC 8335 PROBE messages")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Andreas Roeseler <andreas.a.roeseler@...il.com>
---
 net/ipv4/icmp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index e63a3bf99617627e17669f9b3aaee1cbbf178ebf..e1aaad4bf09cd43d9f3b376416b79a8b2c0a63ca 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -1032,6 +1032,8 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 	struct icmp_ext_hdr *ext_hdr, _ext_hdr;
 	struct icmp_ext_echo_iio *iio, _iio;
 	struct net *net = dev_net(skb->dev);
+	struct inet6_dev *in6_dev;
+	struct in_device *in_dev;
 	struct net_device *dev;
 	char buff[IFNAMSIZ];
 	u16 ident_len;
@@ -1115,10 +1117,15 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 	/* Fill bits in reply message */
 	if (dev->flags & IFF_UP)
 		status |= ICMP_EXT_ECHOREPLY_ACTIVE;
-	if (__in_dev_get_rcu(dev) && __in_dev_get_rcu(dev)->ifa_list)
+
+	in_dev = __in_dev_get_rcu(dev);
+	if (in_dev && rcu_access_pointer(in_dev->ifa_list))
 		status |= ICMP_EXT_ECHOREPLY_IPV4;
-	if (!list_empty(&rcu_dereference(dev->ip6_ptr)->addr_list))
+
+	in6_dev = __in6_dev_get(dev);
+	if (in6_dev && !list_empty(&in6_dev->addr_list))
 		status |= ICMP_EXT_ECHOREPLY_IPV6;
+
 	dev_put(dev);
 	icmphdr->un.echo.sequence |= htons(status);
 	return true;
-- 
2.44.0.769.g3c40516874-goog