net/smc: Prevent kernel-infoleak in __smc_diag_dump()

__smc_diag_dump() is potentially copying uninitialized kernel stack memory
into socket buffers, since the compiler may leave a 4-byte hole near the
beginning of `struct smcd_diag_dmbinfo`. Fix it by initializing `dinfo`
with memset().

Fixes: 4b1b7d3 ("net/smc: add SMC-D diag support")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/smc_diag.c

@@ -170,13 +170,15 @@ static int __smc_diag_dump(struct sock *sk, struct sk_buff *skb,
 	    (req->diag_ext & (1 << (SMC_DIAG_DMBINFO - 1))) &&
 	    !list_empty(&smc->conn.lgr->list)) {
 		struct smc_connection *conn = &smc->conn;
-		struct smcd_diag_dmbinfo dinfo = {
-			.linkid = *((u32 *)conn->lgr->id),
-			.peer_gid = conn->lgr->peer_gid,
-			.my_gid = conn->lgr->smcd->local_gid,
-			.token = conn->rmb_desc->token,
-			.peer_token = conn->peer_token
-		};
+		struct smcd_diag_dmbinfo dinfo;
+
+		memset(&dinfo, 0, sizeof(dinfo));
+
+		dinfo.linkid = *((u32 *)conn->lgr->id);
+		dinfo.peer_gid = conn->lgr->peer_gid;
+		dinfo.my_gid = conn->lgr->smcd->local_gid;
+		dinfo.token = conn->rmb_desc->token;
+		dinfo.peer_token = conn->peer_token;
 
 		if (nla_put(skb, SMC_DIAG_DMBINFO, sizeof(dinfo), &dinfo) < 0)
 			goto errout;