FAILED: patch "[PATCH] gro: ensure frag0 meets IP header alignment" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 38ec4944b593fd90c5ef42aaaa53e66ae5769d04 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <[email protected]>
Date: Tue, 13 Apr 2021 05:41:35 -0700
Subject: [PATCH] gro: ensure frag0 meets IP header alignment

After commit 0f6925b3e8da ("virtio_net: Do not pull payload in skb->head") Guenter Roeck reported one failure in his tests using sh architecture.

After much debugging, we have been able to spot silent unaligned accesses in inet_gro_receive()

The issue at hand is that upper networking stacks assume their header is word-aligned. Low level drivers are supposed to reserve NET_IP_ALIGN bytes before the Ethernet header to make that happen.

This patch hardens skb_gro_reset_offset() to not allow frag0 fast-path if the fragment is not properly aligned.

Some arches like x86, arm64 and powerpc do not care and define NET_IP_ALIGN as 0, this extra check will be a NOP for them.

Note that if frag0 is not used, GRO will call pskb_may_pull() as many times as needed to pull network and transport headers.

index af8c1ea040b9..1f79b9aa9a3f 100644
@@ -5924,7 +5924,8 @@ static void skb_gro_reset_offset(struct sk_buff *skb)
 	NAPI_GRO_CB(skb)->frag0_len = 0;
 
 	if (!skb_headlen(skb) && pinfo->nr_frags &&
-	    !PageHighMem(skb_frag_page(frag0))) {
+	    !PageHighMem(skb_frag_page(frag0)) &&
+	    (!NET_IP_ALIGN || !(skb_frag_off(frag0) & 3))) {
 		NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
 		NAPI_GRO_CB(skb)->frag0_len = min_t(unsigned int,
 						    skb_frag_size(frag0),