[PATCH] net: Avoid unaligned access in inet_gro_receive()

[Helge Deller <deller@kernel.org>]

On the parisc platform the following unaligned accesses are reported regularily:

 Kernel: unaligned access to 0x173d22e76 in inet_gro_receive+0xbc/0x2e8 (iir 0x0e8810b6)
 Kernel: unaligned access to 0x173d22e7e in inet_gro_receive+0xc4/0x2e8 (iir 0x0e88109a)
 Kernel: unaligned access to 0x173d22e82 in inet_gro_receive+0xc8/0x2e8 (iir 0x0e90109d)
 Kernel: unaligned access to 0x173d22e7a in inet_gro_receive+0xd0/0x2e8 (iir 0x0e9810b8)
 Kernel: unaligned access to 0x173d22e86 in inet_gro_receive+0xdc/0x2e8 (iir 0x0e8810b8)

Avoid those unaligned accesses by using the get_unaligned_xx() helpers.
While converting the code, I noticed that while calculating the flush variable
we canuse the 16-bit accessors instead of the 32-bit ones, and the flush
variable should be of type __u16 and doesn't need to be initialized.

Note: Since I don't know the network details, I'm not sure if "~IP_DF"
(~0x4000) is correct, or if "IP_OFFSET" (0x1FFF) should be used instead (which
I think would be more correct). Instead of breaking things I left it as is.

Note 2: Patch still needs runtime testing, so I sent to parisc-linux mailing
list only for now..

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index c7731e300a44..9a0d192b2b35 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1479,7 +1479,7 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
 	struct sk_buff *p;
 	unsigned int hlen;
 	unsigned int off;
-	int flush = 1;
+	__u16 flush;
 	int proto;
 
 	off = skb_gro_offset(skb);
@@ -1504,7 +1504,8 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
 		goto out;
 
 	NAPI_GRO_CB(skb)->proto = proto;
-	flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (ntohl(*(__be32 *)&iph->id) & ~IP_DF));
+	flush = (get_unaligned_be16(&iph->tot_len) ^ skb_gro_len(skb)) |
+	        (get_unaligned_be16(&iph->frag_off) & ~IP_DF);
 
 	list_for_each_entry(p, head, list) {
 		struct iphdr *iph2;
@@ -1519,8 +1520,8 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)
 		 * at the same offset.
 		 */
 		if ((iph->protocol ^ iph2->protocol) |
-		    ((__force u32)iph->saddr ^ (__force u32)iph2->saddr) |
-		    ((__force u32)iph->daddr ^ (__force u32)iph2->daddr)) {
+		    (get_unaligned(&iph->saddr) ^ get_unaligned(&iph2->saddr)) |
+		    (get_unaligned(&iph->daddr) ^ get_unaligned(&iph2->daddr))) {
 			NAPI_GRO_CB(p)->same_flow = 0;
 			continue;
 		}