Commit 7de414a9 authored Nov 01, 2018 by Cong Wang Committed by David S. Miller Nov 01, 2018

net: drop skb on failure in ip_check_defrag()



Most callers of pskb_trim_rcsum() simply drop the skb when
it fails, however, ip_check_defrag() still continues to pass
the skb up to stack. This is suspicious.

In ip_check_defrag(), after we learn the skb is an IP fragment,
passing the skb to callers makes no sense, because callers expect
fragments are defrag'ed on success. So, dropping the skb when we
can't defrag it is reasonable.

Note, prior to commit 88078d98, this is not a big problem as
checksum will be fixed up anyway. After it, the checksum is not
correct on failure.

Found this during code review.

Fixes: 88078d98 ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends")
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 7c6c54b5

net/ipv4/ip_fragment.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -722,10 +722,14 @@ struct sk_buff ip_check_defrag(struct net net, struct sk_buff *skb, u32 user)
		if (ip_is_fragment(&iph)) {
		skb = skb_share_check(skb, GFP_ATOMIC);
		if (skb) {
		if (!pskb_may_pull(skb, netoff + iph.ihl * 4))
		return skb;
		if (pskb_trim_rcsum(skb, netoff + len))
		return skb;
		if (!pskb_may_pull(skb, netoff + iph.ihl * 4)) {
		kfree_skb(skb);
		return NULL;
		}
		if (pskb_trim_rcsum(skb, netoff + len)) {
		kfree_skb(skb);
		return NULL;
		}
		memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
		if (ip_defrag(net, skb, user))
		return NULL;

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