qeth: avoid buffer overflow in snmp ioctl

commit 6fb392b1 upstream.

Check user-defined length in snmp ioctl request and allow request
only if it fits into a qeth command buffer.
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Reviewed-by: Heiko Carstens <heicars2@linux.vnet.ibm.com>
Reported-by: Nico Golde <nico@ngolde.de>
Reported-by: Fabian Yamaguchi <fabs@goesec.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/s390/net/qeth_core_main.c

@@ -4451,7 +4451,7 @@ int qeth_snmp_command(struct qeth_card *card, char __user *udata)
 	struct qeth_cmd_buffer *iob;
 	struct qeth_ipa_cmd *cmd;
 	struct qeth_snmp_ureq *ureq;
-	int req_len;
+	unsigned int req_len;
 	struct qeth_arp_query_info qinfo = {0, };
 	int rc = 0;
 
@@ -4467,6 +4467,10 @@ int qeth_snmp_command(struct qeth_card *card, char __user *udata)
 	/* skip 4 bytes (data_len struct member) to get req_len */
 	if (copy_from_user(&req_len, udata + sizeof(int), sizeof(int)))
 		return -EFAULT;
+	if (req_len > (QETH_BUFSIZE - IPA_PDU_HEADER_SIZE -
+		       sizeof(struct qeth_ipacmd_hdr) -
+		       sizeof(struct qeth_ipacmd_setadpparms_hdr)))
+		return -EINVAL;
 	ureq = memdup_user(udata, req_len + sizeof(struct qeth_snmp_ureq_hdr));
 	if (IS_ERR(ureq)) {
 		QETH_CARD_TEXT(card, 2, "snmpnome");