2 files changed, 9 insertions, 7 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 3edef0bebdd1..910cc29f9e97 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1209,7 +1209,7 @@ extern void tcp_free_md5sig_pool(void);
 extern struct tcp_md5sig_pool   *tcp_get_md5sig_pool(void);
 extern void tcp_put_md5sig_pool(void);
 
-extern int tcp_md5_hash_header(struct tcp_md5sig_pool *, struct tcphdr *);
+extern int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
 extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
                                  unsigned header_len);
 extern int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 704adad8f07f..eefc61e3d0e4 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2994,17 +2994,19 @@ void tcp_put_md5sig_pool(void)
 EXPORT_SYMBOL(tcp_put_md5sig_pool);
 
 int tcp_md5_hash_header(struct tcp_md5sig_pool *hp,
-                        struct tcphdr *th)
+                        const struct tcphdr *th)
 {
         struct scatterlist sg;
+        struct tcphdr hdr;
         int err;
 
-        __sum16 old_checksum = th->check;
-        th->check = 0;
+        /* We are not allowed to change tcphdr, make a local copy */
+        memcpy(&hdr, th, sizeof(hdr));
+        hdr.check = 0;
+
         /* options aren't included in the hash */
-        sg_init_one(&sg, th, sizeof(struct tcphdr));
-        err = crypto_hash_update(&hp->md5_desc, &sg, sizeof(struct tcphdr));
-        th->check = old_checksum;
+        sg_init_one(&sg, &hdr, sizeof(hdr));
+        err = crypto_hash_update(&hp->md5_desc, &sg, sizeof(hdr));
         return err;
 }
 EXPORT_SYMBOL(tcp_md5_hash_header);