[PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

Subsystems: networking [general], networking [tcp], the rest

STALE2567d

3 messages, 3 authors, 2019-07-27 · open the first message on its own page

[PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

From: Jia-Ju Bai <hidden>
Date: 2019-07-26 02:25:44

In inet_csk_rebuild_route(), rt is assigned to NULL on line 1071.
On line 1076, rt is used:
    return &rt->dst;
Thus, a possible null-pointer dereference may occur.

To fix this bug, rt is checked before being used.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <redacted>
---
 net/ipv4/inet_connection_sock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f5c163d4771b..27d9d80f3401 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c

@@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
 		sk_setup_caps(sk, &rt->dst);
 	rcu_read_unlock();
 
-	return &rt->dst;
+	if (rt)
+		return &rt->dst;
+	else
+		return NULL;
 }
 
 struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu)

-- 
2.17.0

Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

From: Nicolas Dichtel <hidden>
Date: 2019-07-26 09:16:01

Le 26/07/2019 à 04:25, Jia-Ju Bai a écrit :

quoted hunk

In inet_csk_rebuild_route(), rt is assigned to NULL on line 1071.
On line 1076, rt is used:
    return &rt->dst;
Thus, a possible null-pointer dereference may occur.>
To fix this bug, rt is checked before being used.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <redacted>
---
 net/ipv4/inet_connection_sock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f5c163d4771b..27d9d80f3401 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c

@@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
 		sk_setup_caps(sk, &rt->dst);
 	rcu_read_unlock();
 
-	return &rt->dst;
+	if (rt)
+		return &rt->dst;
+	else
+		return NULL;

Hmm, ->dst is the first field (and that will never change), thus &rt->dst is
NULL if rt is NULL.
I don't think there is a problem with the current code.


Regards,
Nicolas

Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

From: David Miller <davem@davemloft.net>
Date: 2019-07-27 20:25:13

From: Jia-Ju Bai <redacted>
Date: Fri, 26 Jul 2019 10:25:34 +0800

quoted hunk

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f5c163d4771b..27d9d80f3401 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c

@@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
 		sk_setup_caps(sk, &rt->dst);
 	rcu_read_unlock();
 
-	return &rt->dst;
+	if (rt)
+		return &rt->dst;
+	else
+		return NULL;

If rt is NULL, &rt->dst is also NULL as has been pointed out to you.

Please fix your automated tools to understand this case before submitting
more changes.

Thank you.

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