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Mon, 15 Jun 2026 08:52:36 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 15 Jun 2026 08:52:35 -0700 Message-Id: Cc: "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "John Fastabend" , "Shuah Khan" , , Subject: Re: [PATCH bpf v3 1/2] bpf: Fix packet pointer invalidation for skb dynptr writes From: "Alexei Starovoitov" To: "Yiyang Chen" , X-Mailer: aerc References: In-Reply-To: On Mon Jun 15, 2026 at 7:14 AM PDT, Yiyang Chen wrote: > skb-backed dynptr writer kfuncs can mutate packet data, but the verifier > leaves checked direct packet pointers usable after kfunc calls. > The bpf_dynptr_write() helper already invalidates packet pointers > through clear_all_pkt_pointers(). Make skb dynptr writer kfuncs > follow the same rule. > > Keep two verifier predicates for this. CFG analysis runs before register > states are available, so conservatively mark dynptr writer kfuncs as > packet-changing for subprogram summaries. The normal verifier path uses > the checked dynptr argument and invalidates only when the written dynptr > is, or may be, skb-backed. > > Global subprogram dynptr arguments are prepared as unspecialized local > dynptr pointers, so treat CONST_PTR_TO_DYNPTR local dynptr writer > destinations as possibly packet-backed. This keeps packet pointer > invalidation sound both after global subprogram calls and inside global > subprogram bodies. > > Fixes: daec295a7094 ("bpf/helpers: Introduce bpf_dynptr_copy kfunc") > Fixes: a498ee7576de ("bpf: Implement dynptr copy kfuncs") > Fixes: 5fc5d8fded57 ("bpf: Add bpf_dynptr_memset() kfunc") > Signed-off-by: Yiyang Chen nack. pw-bot: cr