[PATCH net,v3] net/smc: prevent NULL pointer dereference in txopt_get

[Jeongjun Park <aha310510@gmail.com>]

Since smc_inet6_prot does not initialize ipv6_pinfo_offset, inet6_create()
copies an incorrect address value, sk + 0 (offset), to inet_sk(sk)->pinet6.

In addition, since inet_sk(sk)->pinet6 and smc_sk(sk)->clcsock practically
point to the same address, when smc_create_clcsk() stores the newly
created clcsock in smc_sk(sk)->clcsock, inet_sk(sk)->pinet6 is corrupted
into clcsock. This causes NULL pointer dereference and various other
memory corruptions.

To solve this, we need to add a smc6_sock structure for ipv6_pinfo_offset
initialization and modify the smc_sock structure.

Reported-by: syzbot+f69bfae0a4eb29976e44@syzkaller.appspotmail.com
Tested-by: syzbot+f69bfae0a4eb29976e44@syzkaller.appspotmail.com
Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 net/smc/smc.h      | 19 ++++++++++---------
 net/smc/smc_inet.c | 24 +++++++++++++++---------
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/net/smc/smc.h b/net/smc/smc.h
index 34b781e463c4..f4d9338b5ed5 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -284,15 +284,6 @@ struct smc_connection {
 
 struct smc_sock {				/* smc sock container */
 	struct sock		sk;
-	struct socket		*clcsock;	/* internal tcp socket */
-	void			(*clcsk_state_change)(struct sock *sk);
-						/* original stat_change fct. */
-	void			(*clcsk_data_ready)(struct sock *sk);
-						/* original data_ready fct. */
-	void			(*clcsk_write_space)(struct sock *sk);
-						/* original write_space fct. */
-	void			(*clcsk_error_report)(struct sock *sk);
-						/* original error_report fct. */
 	struct smc_connection	conn;		/* smc connection */
 	struct smc_sock		*listen_smc;	/* listen parent */
 	struct work_struct	connect_work;	/* handle non-blocking connect*/
@@ -325,6 +316,16 @@ struct smc_sock {				/* smc sock container */
 						/* protects clcsock of a listen
 						 * socket
 						 * */
+	struct socket		*clcsock;	/* internal tcp socket */
+	void			(*clcsk_state_change)(struct sock *sk);
+						/* original stat_change fct. */
+	void			(*clcsk_data_ready)(struct sock *sk);
+						/* original data_ready fct. */
+	void			(*clcsk_write_space)(struct sock *sk);
+						/* original write_space fct. */
+	void			(*clcsk_error_report)(struct sock *sk);
+						/* original error_report fct. */
+
 };
 
 #define smc_sk(ptr) container_of_const(ptr, struct smc_sock, sk)
diff --git a/net/smc/smc_inet.c b/net/smc/smc_inet.c
index bece346dd8e9..25f34fd65e8d 100644
--- a/net/smc/smc_inet.c
+++ b/net/smc/smc_inet.c
@@ -60,16 +60,22 @@ static struct inet_protosw smc_inet_protosw = {
 };
 
 #if IS_ENABLED(CONFIG_IPV6)
+struct smc6_sock {
+	struct smc_sock smc;
+	struct ipv6_pinfo np;
+};
+
 static struct proto smc_inet6_prot = {
-	.name		= "INET6_SMC",
-	.owner		= THIS_MODULE,
-	.init		= smc_inet_init_sock,
-	.hash		= smc_hash_sk,
-	.unhash		= smc_unhash_sk,
-	.release_cb	= smc_release_cb,
-	.obj_size	= sizeof(struct smc_sock),
-	.h.smc_hash	= &smc_v6_hashinfo,
-	.slab_flags	= SLAB_TYPESAFE_BY_RCU,
+	.name				= "INET6_SMC",
+	.owner				= THIS_MODULE,
+	.init				= smc_inet_init_sock,
+	.hash				= smc_hash_sk,
+	.unhash				= smc_unhash_sk,
+	.release_cb			= smc_release_cb,
+	.obj_size			= sizeof(struct smc6_sock),
+	.h.smc_hash			= &smc_v6_hashinfo,
+	.slab_flags			= SLAB_TYPESAFE_BY_RCU,
+	.ipv6_pinfo_offset		= offsetof(struct smc6_sock, np),
 };
 
 static const struct proto_ops smc_inet6_stream_ops = {
--