From: Junwei Hu <[email protected]>
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 <[email protected]>
Reported-by: Wenhao Zhang <[email protected]>
Reviewed-by: Zhiqiang Liu <[email protected]>
---
net/ipv6/ip6_output.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index edbd12067170..6db3c60b3b66 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
__be32 frag_id;
int ptr, offset = 0, err = 0;
u8 *prevhdr, nexthdr = 0;
+ u8 nexthdr_offset;
err = ip6_find_1stfragopt(skb, &prevhdr);
if (err < 0)
goto fail;
hlen = err;
nexthdr = *prevhdr;
+ nexthdr_offset = prevhdr - skb_network_header(skb);
mtu = ip6_skb_dst_mtu(skb);
@@ -646,6 +648,8 @@ 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);
--
2.19.1
On 03/30/2019 12:29 AM, hujunwei wrote:
> From: Junwei Hu <[email protected]>
>
> 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 <[email protected]>
> Reported-by: Wenhao Zhang <[email protected]>
> Reviewed-by: Zhiqiang Liu <[email protected]>
Interesting.
We got a syzbot report yesterday about this issue. (email thread : BUG: unable to handle kernel paging request in ip6_fragment)
<quote>
syzbot found the following crash on:
HEAD commit: 8c838f53 dpaa2-eth: fix race condition with bql frame acco..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=12b83a9b200000
kernel config: https://syzkaller.appspot.com/x/.config?x=f05902bca21d8935
dashboard link: https://syzkaller.appspot.com/bug?extid=e8ce541d095e486074fc
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
Unfortunately, I don't have any reproducer for this crash yet.
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
</quote>
>
> ---
> net/ipv6/ip6_output.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index edbd12067170..6db3c60b3b66 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
> __be32 frag_id;
> int ptr, offset = 0, err = 0;
> u8 *prevhdr, nexthdr = 0;
> + u8 nexthdr_offset;
>
> err = ip6_find_1stfragopt(skb, &prevhdr);
> if (err < 0)
> goto fail;
> hlen = err;
> nexthdr = *prevhdr;
> + nexthdr_offset = prevhdr - skb_network_header(skb);
>
> mtu = ip6_skb_dst_mtu(skb);
>
> @@ -646,6 +648,8 @@ 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);
>
On 03/30/2019 12:48 AM, Eric Dumazet wrote:
>
>
> On 03/30/2019 12:29 AM, hujunwei wrote:
>> From: Junwei Hu <[email protected]>
>>
>> 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.
>>
...
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index edbd12067170..6db3c60b3b66 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
>> __be32 frag_id;
>> int ptr, offset = 0, err = 0;
>> u8 *prevhdr, nexthdr = 0;
>> + u8 nexthdr_offset;
Why u8 here ?
I would use "unsigned int" really.
>>
>> err = ip6_find_1stfragopt(skb, &prevhdr);
>> if (err < 0)
>> goto fail;
>> hlen = err;
>> nexthdr = *prevhdr;
>> + nexthdr_offset = prevhdr - skb_network_header(skb);
>>
>> mtu = ip6_skb_dst_mtu(skb);
>>
>> @@ -646,6 +648,8 @@ 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);
>>
Hi Eri,
Thanks for your suggestion, u8 may not enough when the packet have a lot of exthdr.
I will update the patch in v2, by the way update Report-by tag.
On 2019/3/30 15:57, Eric Dumazet wrote:
>
> On 03/30/2019 12:48 AM, Eric Dumazet wrote:
>>
>> On 03/30/2019 12:29 AM, hujunwei wrote:
>>> From: Junwei Hu <[email protected]>
>>>
>>> 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.
>>>
> ...
>
>>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>>> index edbd12067170..6db3c60b3b66 100644
>>> --- a/net/ipv6/ip6_output.c
>>> +++ b/net/ipv6/ip6_output.c
>>> @@ -606,12 +606,14 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
>>> __be32 frag_id;
>>> int ptr, offset = 0, err = 0;
>>> u8 *prevhdr, nexthdr = 0;
>>> + u8 nexthdr_offset;
> Why u8 here ?
>
> I would use "unsigned int" really.
>
>>>
>>> err = ip6_find_1stfragopt(skb, &prevhdr);
>>> if (err < 0)
>>> goto fail;
>>> hlen = err;
>>> nexthdr = *prevhdr;
>>> + nexthdr_offset = prevhdr - skb_network_header(skb);
>>>
>>> mtu = ip6_skb_dst_mtu(skb);
>>>
>>> @@ -646,6 +648,8 @@ 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);
>>>
> .
>
From: Junwei Hu <[email protected]>
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 <[email protected]>
Reported-by: Wenhao Zhang <[email protected]>
Reported-by: [email protected]
Reviewed-by: Zhiqiang Liu <[email protected]>
---
V1->V2:
- change nexthdr_offset to unsigned int
- add Reported-by: [email protected]
net/ipv6/ip6_output.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
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);
--
2.19.1
On Sun, Mar 31, 2019 at 05:04:29PM +0800, hujunwei wrote:
> From: Junwei Hu <[email protected]>
>
> 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 <[email protected]>
From: hujunwei <[email protected]>
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.