Re: [PATCH] ipv4: ip_check_defrag must not modify skb before unsharing
From: Eric Leblond <hidden>
Date: 2012-12-10 11:03:42
Also in:
linux-wireless
Possibly related (same subject, not in this thread)
- 2012-12-10 · Re: [PATCH] ipv4: ip_check_defrag must not modify skb before unsharing · David Miller <hidden>
Hello, On Mon, 2012-12-10 at 10:41 +0100, Johannes Berg wrote:
From: Johannes Berg <redacted> 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.
I've applied the patch and built a new kernel. I did not manage to get it crashed when using the two techniques (suspend to ram and down/up interface) that were working well to crash kernel without the patch. BR,
quoted hunk ↗ jump to hunk
Reported-by: Eric Leblond <redacted> Cc: stable@vger.kernel.org Signed-off-by: Johannes Berg <redacted> --- For some versions of the kernel, this code goes into af_packet.c net/ipv4/ip_fragment.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-)diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index 448e685..8d5cc75 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c@@ -707,28 +707,27 @@ 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));
-- Eric Leblond [off-list ref] Blog: https://home.regit.org/