bpf: Fixed segment issue when downgrade gso_size

[PATCH bpf v5] bpf: Fixed segment issue when downgrade gso_size

Posted by Fred Li 1 year, 4 months ago

Linearize skb when downgrad gso_size to prevent triggering
the BUG_ON during segment skb as described in [1].

v5 changes:
 - add bpf subject prefix.
 - adjust message to imperative mood.

v4 changes:
 - add fixed tag.

v3 changes:
 - linearize skb if having frag_list as Willem de Bruijn suggested [2].

[1] https://lore.kernel.org/all/20240626065555.35460-2-dracodingfly@gmail.com/
[2] https://lore.kernel.org/all/668d5cf1ec330_1c18c32947@willemb.c.googlers.com.notmuch/

Fixes: 2be7e212d541 ("bpf: add bpf_skb_adjust_room helper")
Signed-off-by: Fred Li <dracodingfly@gmail.com>
---
 net/core/filter.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index df4578219e82..71396ecfc574 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3525,13 +3525,21 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 	if (skb_is_gso(skb)) {
 		struct skb_shared_info *shinfo = skb_shinfo(skb);
 
-		/* Due to header grow, MSS needs to be downgraded. */
-		if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
-			skb_decrease_gso_size(shinfo, len_diff);
-
 		/* Header must be checked, and gso_segs recomputed. */
 		shinfo->gso_type |= gso_type;
 		shinfo->gso_segs = 0;
+
+		/* Due to header grow, MSS needs to be downgraded.
+		 * There is BUG_ON when segment the frag_list with
+		 * head_frag true so linearize skb after downgrade
+		 * the MSS.
+		 */
+		if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO)) {
+			skb_decrease_gso_size(shinfo, len_diff);
+			if (shinfo->frag_list)
+				return skb_linearize(skb);
+		}
+
 	}
 
 	return 0;
-- 
2.33.0

Re: [PATCH bpf v5] bpf: Fixed segment issue when downgrade gso_size

Posted by Willem de Bruijn 1 year, 4 months ago

On Sun, Jul 21, 2024 at 8:08 PM Fred Li <dracodingfly@gmail.com> wrote:
>
> Linearize skb when downgrad gso_size to prevent triggering
> the BUG_ON during segment skb as described in [1].
>
> v5 changes:
>  - add bpf subject prefix.
>  - adjust message to imperative mood.
>
> v4 changes:
>  - add fixed tag.
>
> v3 changes:
>  - linearize skb if having frag_list as Willem de Bruijn suggested [2].
>
> [1] https://lore.kernel.org/all/20240626065555.35460-2-dracodingfly@gmail.com/
> [2] https://lore.kernel.org/all/668d5cf1ec330_1c18c32947@willemb.c.googlers.com.notmuch/
>
> Fixes: 2be7e212d541 ("bpf: add bpf_skb_adjust_room helper")
> Signed-off-by: Fred Li <dracodingfly@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

My comments were informational, for a next patch if any, really. v4
was fine. v5 is too.

Re: [PATCH bpf v5] bpf: Fixed segment issue when downgrade gso_size

Posted by Fred Li 1 year, 4 months ago

> >
> > Linearize skb when downgrad gso_size to prevent triggering
> > the BUG_ON during segment skb as described in [1].
> >
> > v5 changes:
> >  - add bpf subject prefix.
> >  - adjust message to imperative mood.
> >
> > v4 changes:
> >  - add fixed tag.
> >
> > v3 changes:
> >  - linearize skb if having frag_list as Willem de Bruijn suggested [2].
> >
> > [1] https://lore.kernel.org/all/20240626065555.35460-2-dracodingfly@gmail.com/
> > [2] https://lore.kernel.org/all/668d5cf1ec330_1c18c32947@willemb.c.googlers.com.notmuch/
> >
> > Fixes: 2be7e212d541 ("bpf: add bpf_skb_adjust_room helper")
> > Signed-off-by: Fred Li <dracodingfly@gmail.com>
> 
> Reviewed-by: Willem de Bruijn <willemb@google.com>
> 
> My comments were informational, for a next patch if any, really. v4
> was fine. v5 is too.

Thanks for your advise.

Fred Li

Re: [PATCH bpf v5] bpf: Fixed segment issue when downgrade gso_size

Posted by Daniel Borkmann 1 year, 4 months ago

On 7/24/24 3:37 PM, Fred Li wrote:
>>>
>>> Linearize skb when downgrad gso_size to prevent triggering
>>> the BUG_ON during segment skb as described in [1].
>>>
>>> v5 changes:
>>>   - add bpf subject prefix.
>>>   - adjust message to imperative mood.
>>>
>>> v4 changes:
>>>   - add fixed tag.
>>>
>>> v3 changes:
>>>   - linearize skb if having frag_list as Willem de Bruijn suggested [2].
>>>
>>> [1] https://lore.kernel.org/all/20240626065555.35460-2-dracodingfly@gmail.com/
>>> [2] https://lore.kernel.org/all/668d5cf1ec330_1c18c32947@willemb.c.googlers.com.notmuch/
>>>
>>> Fixes: 2be7e212d541 ("bpf: add bpf_skb_adjust_room helper")
>>> Signed-off-by: Fred Li <dracodingfly@gmail.com>
>>
>> Reviewed-by: Willem de Bruijn <willemb@google.com>
>>
>> My comments were informational, for a next patch if any, really. v4
>> was fine. v5 is too.
> 
> Thanks for your advise.
> 
> Fred Li

lgtm, I slightly improved wording & applied, thanks!