net/smc: check for missing nlattrs in SMC_PNETID messages

It's possible to crash the kernel in several different ways by sending
messages to the SMC_PNETID generic netlink family that are missing the
expected attributes:

- Missing SMC_PNETID_NAME => null pointer dereference when comparing
  names.
- Missing SMC_PNETID_ETHNAME => null pointer dereference accessing
  smc_pnetentry::ndev.
- Missing SMC_PNETID_IBNAME => null pointer dereference accessing
  smc_pnetentry::smcibdev.
- Missing SMC_PNETID_IBPORT => out of bounds array access to
  smc_ib_device::pattr[-1].

Fix it by validating that all expected attributes are present and that
SMC_PNETID_IBPORT is nonzero.

Reported-by: syzbot+5cd61039dc9b8bfa6e47@syzkaller.appspotmail.com
Fixes: 6812baab ("smc: establish pnet table management")
Cc: <stable@vger.kernel.org> # v4.11+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/smc_pnet.c

@@ -245,40 +245,45 @@ static struct smc_ib_device *smc_pnet_find_ib(char *ib_name)
 static int smc_pnet_fill_entry(struct net *net, struct smc_pnetentry *pnetelem,
 			       struct nlattr *tb[])
 {
-	char *string, *ibname = NULL;
-	int rc = 0;
+	char *string, *ibname;
+	int rc;
 
 	memset(pnetelem, 0, sizeof(*pnetelem));
 	INIT_LIST_HEAD(&pnetelem->list);
-	if (tb[SMC_PNETID_NAME]) {
+
+	rc = -EINVAL;
+	if (!tb[SMC_PNETID_NAME])
+		goto error;
 	string = (char *)nla_data(tb[SMC_PNETID_NAME]);
-		if (!smc_pnetid_valid(string, pnetelem->pnet_name)) {
+	if (!smc_pnetid_valid(string, pnetelem->pnet_name))
+		goto error;
+
 	rc = -EINVAL;
+	if (!tb[SMC_PNETID_ETHNAME])
 		goto error;
-		}
-	}
-	if (tb[SMC_PNETID_ETHNAME]) {
+	rc = -ENOENT;
 	string = (char *)nla_data(tb[SMC_PNETID_ETHNAME]);
 	pnetelem->ndev = dev_get_by_name(net, string);
 	if (!pnetelem->ndev)
-			return -ENOENT;
-	}
-	if (tb[SMC_PNETID_IBNAME]) {
+		goto error;
+
+	rc = -EINVAL;
+	if (!tb[SMC_PNETID_IBNAME])
+		goto error;
+	rc = -ENOENT;
 	ibname = (char *)nla_data(tb[SMC_PNETID_IBNAME]);
 	ibname = strim(ibname);
 	pnetelem->smcibdev = smc_pnet_find_ib(ibname);
-		if (!pnetelem->smcibdev) {
-			rc = -ENOENT;
+	if (!pnetelem->smcibdev)
 		goto error;
-		}
-	}
-	if (tb[SMC_PNETID_IBPORT]) {
-		pnetelem->ib_port = nla_get_u8(tb[SMC_PNETID_IBPORT]);
-		if (pnetelem->ib_port > SMC_MAX_PORTS) {
+
 	rc = -EINVAL;
+	if (!tb[SMC_PNETID_IBPORT])
 		goto error;
-		}
-	}
+	pnetelem->ib_port = nla_get_u8(tb[SMC_PNETID_IBPORT]);
+	if (pnetelem->ib_port < 1 || pnetelem->ib_port > SMC_MAX_PORTS)
+		goto error;
+
 	return 0;
 
 error:
@@ -307,6 +312,8 @@ static int smc_pnet_get(struct sk_buff *skb, struct genl_info *info)
 	void *hdr;
 	int rc;
 
+	if (!info->attrs[SMC_PNETID_NAME])
+		return -EINVAL;
 	pnetelem = smc_pnet_find_pnetid(
 				(char *)nla_data(info->attrs[SMC_PNETID_NAME]));
 	if (!pnetelem)
@@ -359,6 +366,8 @@ static int smc_pnet_add(struct sk_buff *skb, struct genl_info *info)
 
 static int smc_pnet_del(struct sk_buff *skb, struct genl_info *info)
 {
+	if (!info->attrs[SMC_PNETID_NAME])
+		return -EINVAL;
 	return smc_pnet_remove_by_pnetid(
 				(char *)nla_data(info->attrs[SMC_PNETID_NAME]));
 }