Re: [PATCH bpf] bpf: free page_pool frags via the page_pool path in bpf_xdp_shrink_data

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 8/16/26 11:37 AM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] The netmem_is_pp() check fails on compound tail pages, leading to page_pool leaks and 'Bad page state' kernel panics.
> - [Low] The multi-line comment introduced in bpf_xdp_shrink_data() does not follow the required BPF subsystem comment style.
> --
>
> --- Patch [1]: [PATCH bpf] bpf: free page_pool frags via the page_pool path in bpf_xdp_shrink_data ---
> commit 28e0b86b119236ed1263628b895946efb16e99cf
> Author: Jiayuan Chen <jiayuan.chen@linux.dev>
>
> bpf: free page_pool frags via the page_pool path in bpf_xdp_shrink_data
>
> This commit fixes a page_pool leak reported by syzbot when generic XDP
> programs shrink skbs into fragments. It inspects the page itself using
> netmem_is_pp() rather than relying on the rxq memory model.
>
> Closes: https://syzkaller.appspot.com/bug?extid=237bbeed8dfe0699b7f5
>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 3423734124a5b..4536bd147c253 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
> [ ... ]
>
>> @@ -4293,6 +4294,14 @@ static bool bpf_xdp_shrink_data(struct xdp_buff *xdp, skb_frag_t *frag,
>>   	if (mem_type == MEM_TYPE_XSK_BUFF_POOL) {
>>   		netmem = 0;
>>   		zc_frag = bpf_xdp_shrink_data_zc(xdp, shrink, tail, release);
>> +	} else if (netmem_is_pp(netmem)) {
> [Severity: High]
> Does this check handle compound tail pages correctly?

I think we should process it like napi_pp_put_page

...

   } else if (netmem_is_pp(netmem_compound_head(netmem))) {
       mem_type = MEM_TYPE_PAGE_POOL;
   }