[PATCH] ipv6: frags: Fix bogus skb->sk in reassembled packets

It was reported that IPsec would crash when it encounters an IPv6
reassembled packet because skb->sk is non-zero and not a valid
pointer.

This is because skb->sk is now a union with ip_defrag_offset.

This patch fixes this by resetting skb->sk when exiting from
the reassembly code.

Reported-by: Xiumei Mu <redacted>
Fixes: 219badfaade9 ("ipv6: frags: get rid of ip6frag_skb_cb/...")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 5c3c92713096..a98f95fb6eac 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c

@@ -378,6 +378,7 @@ static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
 		if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
 			kfree_skb_partial(fp, headstolen);
 		} else {
+			fp->sk = NULL;
 			if (!skb_shinfo(head)->frag_list)
 				skb_shinfo(head)->frag_list = fp;
 			head->data_len += fp->len;

-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

On Thu, Dec 20, 2018 at 5:20 AM Herbert Xu [off-list ref] wrote:

I wonder why this have not been done earlier in commit

commit 5d407b071dc369c26a38398326ee2be53651cfe4
Author: Taehee Yoo [off-list ref]
Date:   Mon Sep 10 02:47:05 2018 +0900

    ip: frags: fix crash in ip_do_fragment()

Maybe because the Fixes tag mentioned fa0f527358bd ("ip: use rb trees
for IP frag queue.")
and IPv6 reasm was not using rbtree ...

Oh well.

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu, 20 Dec 2018 21:20:10 +0800

It was reported that IPsec would crash when it encounters an IPv6
reassembled packet because skb->sk is non-zero and not a valid
pointer.

This is because skb->sk is now a union with ip_defrag_offset.

This patch fixes this by resetting skb->sk when exiting from
the reassembly code.

Reported-by: Xiumei Mu <redacted>
Fixes: 219badfaade9 ("ipv6: frags: get rid of ip6frag_skb_cb/...")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Applied and queued up for -stable, thanks Herbert.