[PATCH net] crypto: chtls: Fix possible null pointer dereferences

[Aleksandr Mishin]

In chtls_pass_accept_rpl() and chtls_select_mss() __sk_dst_get() may
return NULL which is later dereferenced. Fix this bug by adding NULL check.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: cc35c88ae4db ("crypto : chtls - CPL handler definition")
Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>
---
 .../chelsio/inline_crypto/chtls/chtls_cm.c    | 24 +++++++++++++------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
index 6f6525983130..6d88cbc9fbb0 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
@@ -939,15 +939,15 @@ static void chtls_accept_rpl_arp_failure(void *handle,
 	sock_put(sk);
 }
 
-static unsigned int chtls_select_mss(const struct chtls_sock *csk,
+static bool chtls_select_mss(const struct chtls_sock *csk,
 				     unsigned int pmtu,
-				     struct cpl_pass_accept_req *req)
+				     struct cpl_pass_accept_req *req,
+					 unsigned int *mtu_idx)
 {
 	struct chtls_dev *cdev;
 	struct dst_entry *dst;
 	unsigned int tcpoptsz;
 	unsigned int iphdrsz;
-	unsigned int mtu_idx;
 	struct tcp_sock *tp;
 	unsigned int mss;
 	struct sock *sk;
@@ -955,6 +955,9 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
 	mss = ntohs(req->tcpopt.mss);
 	sk = csk->sk;
 	dst = __sk_dst_get(sk);
+	if (!dst)
+		return false;
+
 	cdev = csk->cdev;
 	tp = tcp_sk(sk);
 	tcpoptsz = 0;
@@ -979,11 +982,11 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
 	tp->advmss = cxgb4_best_aligned_mtu(cdev->lldi->mtus,
 					    iphdrsz + tcpoptsz,
 					    tp->advmss - tcpoptsz,
-					    8, &mtu_idx);
+					    8, mtu_idx);
 	tp->advmss -= iphdrsz;
 
 	inet_csk(sk)->icsk_pmtu_cookie = pmtu;
-	return mtu_idx;
+	return true;
 }
 
 static unsigned int select_rcv_wscale(int space, int wscale_ok, int win_clamp)
@@ -1016,8 +1019,13 @@ static void chtls_pass_accept_rpl(struct sk_buff *skb,
 	struct sock *sk;
 	u32 opt2, hlen;
 	u64 opt0;
+	struct dst_entry *dst;
 
 	sk = skb->sk;
+	dst = __sk_dst_get(sk);
+	if (!dst)
+		return;
+
 	tp = tcp_sk(sk);
 	csk = sk->sk_user_data;
 	csk->tid = tid;
@@ -1029,8 +1037,10 @@ static void chtls_pass_accept_rpl(struct sk_buff *skb,
 
 	OPCODE_TID(rpl5) = cpu_to_be32(MK_OPCODE_TID(CPL_PASS_ACCEPT_RPL,
 						     csk->tid));
-	csk->mtu_idx = chtls_select_mss(csk, dst_mtu(__sk_dst_get(sk)),
-					req);
+	if (!chtls_select_mss(csk, dst_mtu(dst),
+					req, &csk->mtu_idx))
+		return;
+
 	opt0 = TCAM_BYPASS_F |
 	       WND_SCALE_V(RCV_WSCALE(tp)) |
 	       MSS_IDX_V(csk->mtu_idx) |
-- 
2.30.2