net: tso: fix unaligned access to crafted TCP header in helper API

commit a63ba13e upstream.

The crafted header start address is from a driver supplied buffer, which
one can reasonably expect to be aligned on a 4-bytes boundary.
However ATM the TSO helper API is only used by ethernet drivers and
the tcp header will then be aligned to a 2-bytes only boundary from the
header start address.
Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/core/tso.c

 #include <linux/export.h>
 #include <net/ip.h>
 #include <net/tso.h>
+#include <asm/unaligned.h>
 
 /* Calculate expected number of TX descriptors */
 int tso_count_descs(struct sk_buff *skb)
@@ -23,7 +24,7 @@ void tso_build_hdr(struct sk_buff *skb, char *hdr, struct tso_t *tso,
 	iph->id = htons(tso->ip_id);
 	iph->tot_len = htons(size + hdr_len - mac_hdr_len);
 	tcph = (struct tcphdr *)(hdr + skb_transport_offset(skb));
-	tcph->seq = htonl(tso->tcp_seq);
+	put_unaligned_be32(tso->tcp_seq, &tcph->seq);
 	tso->ip_id++;
 
 	if (!is_last) {