ioam6_fill_trace_data() writes inside the skb payload without ensuring
it's writeable (e.g., not cloned). This function is called both from the
input and output path. The output path (ioam6_iptunnel) already does the
check. This commit provides a fix for the input path, inside
ipv6_hop_ioam().

Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace ")
Reported-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
---
 net/ipv6/exthdrs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 4952ae792450..f68e5faab3aa 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -943,6 +943,14 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
 		if (!skb_valid_dst(skb))
 			ip6_route_input(skb);
 
+		if (skb_cloned(skb)) {
+			if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+				goto drop;
+
+			hdr = (struct ioam6_hdr *)(skb_network_header(skb) + optoff);
+			trace = (struct ioam6_trace_hdr *)((u8 *)hdr + sizeof(*hdr));
+		}
+
 		ioam6_fill_trace_data(skb, ns, trace, true);
 		break;
 	default:
-- 
2.34.1

On Sat, 2024-02-17 at 00:43 +0100, Justin Iurman wrote:
> ioam6_fill_trace_data() writes inside the skb payload without ensuring
> it's writeable (e.g., not cloned). This function is called both from the
> input and output path. The output path (ioam6_iptunnel) already does the
> check. This commit provides a fix for the input path, inside
> ipv6_hop_ioam().
> 
> Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace ")
> Reported-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
> ---
>  net/ipv6/exthdrs.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 4952ae792450..f68e5faab3aa 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -943,6 +943,14 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
>  		if (!skb_valid_dst(skb))
>  			ip6_route_input(skb);
>  
> +		if (skb_cloned(skb)) {
> +			if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
> +				goto drop;

My personal preference would be for using skb_ensure_writable() here,
with write_len == optoff + hdr->opt_len.

> +
> +			hdr = (struct ioam6_hdr *)(skb_network_header(skb) + optoff);
> +			trace = (struct ioam6_trace_hdr *)((u8 *)hdr + sizeof(*hdr));

Note that this can potentially change the network header ptr and the
caller - ip6_parse_tlv() - has cached such value in 'nh'. You also need
to update ip6_parse_tlv() to reload such pointer.

Side note: a bunch of self-tests are apparently stuck after this
series. I think it's an unrelated problem. I'll try to have a better
look.

Cheers,

Paolo

On 2/19/24 10:05, Paolo Abeni wrote:
> On Sat, 2024-02-17 at 00:43 +0100, Justin Iurman wrote:
>> ioam6_fill_trace_data() writes inside the skb payload without ensuring
>> it's writeable (e.g., not cloned). This function is called both from the
>> input and output path. The output path (ioam6_iptunnel) already does the
>> check. This commit provides a fix for the input path, inside
>> ipv6_hop_ioam().
>>
>> Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace ")
>> Reported-by: Paolo Abeni <pabeni@redhat.com>
>> Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
>> ---
>>   net/ipv6/exthdrs.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
>> index 4952ae792450..f68e5faab3aa 100644
>> --- a/net/ipv6/exthdrs.c
>> +++ b/net/ipv6/exthdrs.c
>> @@ -943,6 +943,14 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
>>   		if (!skb_valid_dst(skb))
>>   			ip6_route_input(skb);
>>   
>> +		if (skb_cloned(skb)) {
>> +			if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
>> +				goto drop;
> 
> My personal preference would be for using skb_ensure_writable() here,
> with write_len == optoff + hdr->opt_len.

OK, will do!

>> +
>> +			hdr = (struct ioam6_hdr *)(skb_network_header(skb) + optoff);
>> +			trace = (struct ioam6_trace_hdr *)((u8 *)hdr + sizeof(*hdr));
> 
> Note that this can potentially change the network header ptr and the
> caller - ip6_parse_tlv() - has cached such value in 'nh'. You also need
> to update ip6_parse_tlv() to reload such pointer.

+1, I completely missed it, thanks!

> Side note: a bunch of self-tests are apparently stuck after this
> series. I think it's an unrelated problem. I'll try to have a better
> look.

Can you share the config to observe such behavior? I'll try to 
investigate too.

> Cheers,
> 
> Paolo
>