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Miller" , "Eric Dumazet" , "Jakub Kicinski" , "Paolo Abeni" , "Simon Horman" , , Subject: Re: [PATCH bpf] bpf: Fix verifier WARN on narrow read of bpf_tcp_sock u64 fields In-Reply-To: <20261016111643.247553-1-jiayuan.chen@linux.dev> References: <20261016111643.247553-1-jiayuan.chen@linux.dev> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, Oct 16, 2026 at 07:16 PM Jiayuan Chen wrote: > Just disallow the narrower access by matching the whole u64 range of the > two fields, so it is turned down at check time: > > invalid tcp_sock access off=84 size=4 Pls add a selftest as patch 2. progs/verifier_sock.c already has "bpf_tcp_sock(skb->sk): tp->bytes_acked". Copy it and do u32 load at offsetof(bytes_received) + 4 and at offsetof(bytes_acked) + 4 with __failure __msg("invalid tcp_sock access") __failure_unpriv. cgroup/skb is loadable by unpriv, so both modes should be covered. See commit ba578b87fe2b ("selftests/bpf: Test invalid narrower ctx load") that Paul added for the same warn in ctx fields. I'm hesitating to apply it as-is, since all earlier fixes for this warn came with a test. pw-bot: cr