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net: drop dst before queueing fragments

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[ Upstream commit 97599dc792 ]

Commit 4a94445c9a (net: Use ip_route_input_noref() in input path)
added a bug in IP defragmentation handling, as non refcounted
dst could escape an RCU protected section.

Commit 64f3b9e203 (net: ip_expire() must revalidate route) fixed
the case of timeouts, but not the general problem.

Tom Parkin noticed crashes in UDP stack and provided a patch,
but further analysis permitted us to pinpoint the root cause.

Before queueing a packet into a frag list, we must drop its dst,
as this dst has limited lifetime (RCU protected)

When/if a packet is finally reassembled, we use the dst of the very
last skb, still protected by RCU and valid, as the dst of the
reassembled packet.

Use same logic in IPv6, as there is no need to hold dst references.

Reported-by: Tom Parkin <tparkin@katalix.com>
Tested-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric Dumazet 2013-04-16 12:55:41 +00:00 committed by Greg Kroah-Hartman
parent ca4bf7c697
commit 1d0dd1db15
2 changed files with 22 additions and 6 deletions
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15
net/ipv4/ip_fragment.c
View File

@ -251,8 +251,7 @@ static void ip_expire(unsigned long arg)
if (!head->dev)
goto out_rcu_unlock;
/* skb dst is stale, drop it, and perform route lookup again */
skb_dst_drop(head);
/* skb has no dst, perform route lookup again */
iph = ip_hdr(head);
err = ip_route_input_noref(head, iph->daddr, iph->saddr,
iph->tos, head->dev);
@ -517,8 +516,16 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
qp->q.last_in |= INET_FRAG_FIRST_IN;
if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
qp->q.meat == qp->q.len)
return ip_frag_reasm(qp, prev, dev);
qp->q.meat == qp->q.len) {
unsigned long orefdst = skb->_skb_refdst;
skb->_skb_refdst = 0UL;
err = ip_frag_reasm(qp, prev, dev);
skb->_skb_refdst = orefdst;
return err;
}
skb_dst_drop(skb);
write_lock(&ip4_frags.lock);
list_move_tail(&qp->q.lru_list, &qp->q.net->lru_list);

13
net/ipv6/reassembly.c
View File

@ -385,8 +385,17 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
}
if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
fq->q.meat == fq->q.len)
return ip6_frag_reasm(fq, prev, dev);
fq->q.meat == fq->q.len) {
int res;
unsigned long orefdst = skb->_skb_refdst;
skb->_skb_refdst = 0UL;
res = ip6_frag_reasm(fq, prev, dev);
skb->_skb_refdst = orefdst;
return res;
}
skb_dst_drop(skb);
write_lock(&ip6_frags.lock);
list_move_tail(&fq->q.lru_list, &fq->q.net->lru_list);