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[v2,net] ipv6: Fix dangling pointer when ipv6 fragment

Message ID 9104f44b-2ce0-7be9-2fca-8b6c12abbb86@huawei.com
State Changes Requested
Delegated to: David Miller
Headers show
Series [v2,net] ipv6: Fix dangling pointer when ipv6 fragment | expand

Commit Message

hujunwei March 31, 2019, 9:04 a.m. UTC 
From: Junwei Hu <hujunwei4@huawei.com>

At the beginning of ip6_fragment func, the prevhdr pointer is
obtained in the ip6_find_1stfragopt func.
However, all the pointers pointing into skb header may change
when calling skb_checksum_help func with
skb->ip_summed = CHECKSUM_PARTIAL condition.
The prevhdr pointe will be dangling if it is not reloaded after
calling __skb_linearize func in skb_checksum_help func.

Here, I add a variable, nexthdr_offset, to evaluate the offset,
which does not changes even after calling __skb_linearize func.

Fixes: 405c92f7a541 ("ipv6: add defensive check for CHECKSUM_PARTIAL skbs in ip_fragment")
Signed-off-by: Junwei Hu <hujunwei4@huawei.com>
Reported-by: Wenhao Zhang <zhangwenhao8@huawei.com>
Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com
Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
---
V1->V2:
- change nexthdr_offset to unsigned int
- add Reported-by: syzbot+e8ce541d095e486074fc@syzkaller.appspotmail.com

 net/ipv6/ip6_output.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Martin KaFai Lau April 1, 2019, 4:34 p.m. UTC | #1 
On Sun, Mar 31, 2019 at 05:04:29PM +0800, hujunwei wrote:
> From: Junwei Hu <hujunwei4@huawei.com>
> 
> At the beginning of ip6_fragment func, the prevhdr pointer is
> obtained in the ip6_find_1stfragopt func.
> However, all the pointers pointing into skb header may change
> when calling skb_checksum_help func with
> skb->ip_summed = CHECKSUM_PARTIAL condition.
> The prevhdr pointe will be dangling if it is not reloaded after
> calling __skb_linearize func in skb_checksum_help func.
> 
> Here, I add a variable, nexthdr_offset, to evaluate the offset,
> which does not changes even after calling __skb_linearize func.
Acked-by: Martin KaFai Lau <kafai@fb.com>
David Miller April 2, 2019, 1:12 a.m. UTC | #2 
From: hujunwei <hujunwei4@huawei.com>
Date: Sun, 31 Mar 2019 17:04:29 +0800

> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index edbd12067170..e51f3c648b09 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -601,7 +601,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
>                  inet6_sk(skb->sk) : NULL;
>      struct ipv6hdr *tmp_hdr;
>      struct frag_hdr *fh;
> -    unsigned int mtu, hlen, left, len;

Your patch was corrupted by your email client.

Please fix this, email a test patch to yourself, and only when you can
successfully apply that test patch should you repost this to the mailing
list.

Thank you.
diff mbox series

Patch

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index edbd12067170..e51f3c648b09 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -601,7 +601,7 @@  int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
                 inet6_sk(skb->sk) : NULL;
     struct ipv6hdr *tmp_hdr;
     struct frag_hdr *fh;
-    unsigned int mtu, hlen, left, len;
+    unsigned int mtu, hlen, left, len, nexthdr_offset;
     int hroom, troom;
     __be32 frag_id;
     int ptr, offset = 0, err = 0;
@@ -612,6 +612,7 @@  int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
         goto fail;
     hlen = err;
     nexthdr = *prevhdr;
+    nexthdr_offset = prevhdr - skb_network_header(skb);
 
     mtu = ip6_skb_dst_mtu(skb);
 
@@ -646,6 +647,7 @@  int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
         (err = skb_checksum_help(skb)))
         goto fail;
 
+    prevhdr = skb_network_header(skb) + nexthdr_offset;
     hroom = LL_RESERVED_SPACE(rt->dst.dev);
     if (skb_has_frag_list(skb)) {
         unsigned int first_len = skb_pagelen(skb);