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net: drop skb on failure in ip_check_defrag()

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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 88078d98d1, 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: 88078d98d1 ("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>
This commit is contained in:
Cong Wang 2018-11-01 12:02:37 -07:00 committed by David S. Miller
parent 7c6c54b505
commit 7de414a9dd
1 changed files with 8 additions and 4 deletions
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12
net/ipv4/ip_fragment.c
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@ -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;