2019-07-26 02:27:16

by Jia-Ju Bai

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

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 <[email protected]>
---
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

2019-07-26 09:16:51

by Nicolas Dichtel

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

Le 26/07/2019 à 04:25, Jia-Ju Bai a écrit :
> 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 <[email protected]>
> ---
> 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

2019-07-27 20:27:06

by David Miller

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

From: Jia-Ju Bai <[email protected]>
Date: Fri, 26 Jul 2019 10:25:34 +0800

> 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.