chelsio/chtls: prevent potential integer overflow on 32bit

The "gl->tot_len" variable is controlled by the user.  It comes from
process_responses().  On 32bit systems, the "gl->tot_len +
sizeof(struct cpl_pass_accept_req) + sizeof(struct rss_header)" addition
could have an integer wrapping bug.  Use size_add() to prevent this.

Fixes: a089439 ("crypto: chtls - Register chtls with net tls")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/c6bfb23c-2db2-4e1b-b8ab-ba3925c82ef5@stanley.mountain
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Dan Carpenter

drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_main.c

@@ -346,8 +346,9 @@ static struct sk_buff *copy_gl_to_skb_pkt(const struct pkt_gl *gl,
 	 * driver. Once driver synthesizes cpl_pass_accept_req the skb will go
 	 * through the regular cpl_pass_accept_req processing in TOM.
 	 */
-	skb = alloc_skb(gl->tot_len + sizeof(struct cpl_pass_accept_req)
-			- pktshift, GFP_ATOMIC);
+	skb = alloc_skb(size_add(gl->tot_len,
+				 sizeof(struct cpl_pass_accept_req)) -
+			pktshift, GFP_ATOMIC);
 	if (unlikely(!skb))
 		return NULL;
 	__skb_put(skb, gl->tot_len + sizeof(struct cpl_pass_accept_req)