linux-kernel - Re: [PATCH] bpf: restrict verifier access to bpf_lru

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Message-ID: <4c9fcc40-9aca-4ac8-9769-1075e2858b8a@linux.dev>
Date: Wed, 16 Jul 2025 13:02:33 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Shankari Anand <shankari.ak0208@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
 bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Martin KaFai Lau <martin.lau@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 syzbot+ad4661d6ca888ce7fe11@...kaller.appspotmail.com,
 Hou Tao <hotforest@...il.com>
Subject: Re: [PATCH] bpf: restrict verifier access to bpf_lru_node.ref

On 7/15/25 11:32 PM, Shankari Anand wrote:
>> I think the percpu_freelist used in the regular hashmap should have similar
>> behavior, so may be worth finding a common solution, such as waiting for a rcu
>> gp before reusing it.
> To resolve this, would it make sense to ensure that elements popped
> from the free list are only reused after a grace period? Similar to
> how other parts of the kernel manage safe object reuse.

The reuse behavior has been there for a long time. It had been discussed
before. Please go back to those threads for the background
and the direction that it is going. This thread is a good start:

https://lore.kernel.org/bpf/20250204082848.13471-3-hotforest@gmail.com/