[ 07/80] ipv4: ip_check_defrag must not modify skb before unsharing

Greg Kroah-Hartman
2013-01-09T21:44:50Z

From: Johannes Berg <johannes.berg@intel.com>

[ Upstream commit 1bf3751ec90cc3174e01f0d701e8449ce163d113 ]

ip_check_defrag() might be called from af_packet within the
RX path where shared SKBs are used, so it must not modify
the input SKB before it has unshared it for defragmentation.
Use skb_copy_bits() to get the IP header and only pull in
everything later.

The same is true for the other caller in macvlan as it is
called from dev->rx_handler which can also get a shared SKB.

Reported-by: Eric Leblond <eric@regit.org>
Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_fragment.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -685,28 +685,27 @@ EXPORT_SYMBOL(ip_defrag);

struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user)
{
- const struct iphdr *iph;
+ struct iphdr iph;
u32 len;

if (skb->protocol != htons(ETH_P_IP))
return skb;

- if (!pskb_may_pull(skb, sizeof(struct iphdr)))
+ if (!skb_copy_bits(skb, 0, &iph, sizeof(iph)))
return skb;

- iph = ip_hdr(skb);
- if (iph->ihl < 5 || iph->version != 4)
+ if (iph.ihl < 5 || iph.version != 4)
return skb;
- if (!pskb_may_pull(skb, iph->ihl*4))
- return skb;
- iph = ip_hdr(skb);
- len = ntohs(iph->tot_len);
- if (skb->len < len || len < (iph->ihl * 4))
+
+ len = ntohs(iph.tot_len);
+ if (skb->len < len || len < (iph.ihl * 4))
return skb;

- if (ip_is_fragment(ip_hdr(skb))) {
+ if (ip_is_fragment(&iph)) {
skb = skb_share_check(skb, GFP_ATOMIC);
if (skb) {
+ if (!pskb_may_pull(skb, iph.ihl*4))
+ return skb;
if (pskb_trim_rcsum(skb, len))
return skb;
memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));