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Tue, 03 Nov 2026 17:05:38 -0800 (PST) Received: from localhost ([153.61.198.241]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b0944d1a43sm1272825a91.13.2026.11.03.17.05.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2026 17:05:37 -0800 (PST) Content-Type: text/plain; charset=UTF-8 Date: Wed, 04 Nov 2026 01:05:37 +0000 Message-Id: Subject: Re: [PATCH bpf-next 06/37] bpf: Count stack arguments of a static subprog from its code From: "Alexei Starovoitov" To: , In-Reply-To: References: <20261103234104.208239-1-alexei.starovoitov@gmail.com> <20261103234104.208239-7-alexei.starovoitov@gmail.com> Content-Transfer-Encoding: 8bit X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Tue, Nov 03, 2026 at 04:14 PM sashiko-bot@kernel.org wrote: >> + stack_arg_cnt = bpf_in_stack_arg_cnt(caller_info) + >> + max_t(int, callee_incoming, >> + min_t(int, caller_info->max_out_stack_arg_cnt, >> + callee_info->arg_slot_cnt - MAX_BPF_FUNC_REG_ARGS)); > > [Severity: Medium] > Can btf_prepare_func_args() leave sub->arg_slot_cnt undercounted when it > returns early on a static subprogram with multi-slot parameters? [...] > using the parameter count rather than the slot count. Because this > undercounts the prototype's stack argument slots, wouldn't > bpf_fixup_call_args() reject valid caller stores to those trailing stack > argument slots? Not from this patch. bpf-next has arg_slot_cnt == nargs after an early return too, and bpf_fixup_call_args() rejects the same store with the same message. bpf-next also rejects the load of such a slot in the callee.