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Sat, 31 Oct 2026 10:03:06 -0700 (PDT) Received: from localhost ([153.61.198.246]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8aadad94a8esm817264b3a.55.2026.10.31.10.03.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 31 Oct 2026 10:03:05 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 31 Oct 2026 17:03:04 +0000 Message-Id: Cc: "Ihor Solodrai" , "Alan Maguire" , "Martin KaFai Lau" , "Yonghong Song" , "Jiri Olsa" , "Steven Rostedt" , "Masami Hiramatsu" , "Mathieu Desnoyers" , , "Nathan Chancellor" , "Nicolas Schier" , , "Arnd Bergmann" , , , , , "Hazem Mohamed Abuelfotoh" , "Bjoern Doebel" , "Martin Pohlack" , Subject: Re: [PATCH bpf-next 03/13] bpf: check CAP_SYS_ADMIN before looking up bpffs delegation names From: "Alexei Starovoitov" To: "Jay Wang" , , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" In-Reply-To: <20261031130959.23472-4-wanjay@amazon.com> References: <20261031130959.23472-1-wanjay@amazon.com> <20261031130959.23472-4-wanjay@amazon.com> Content-Transfer-Encoding: 8bit X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Sat, Oct 31, 2026 at 06:09 AM Jay Wang wrote: > That is free today because the vmlinux BTF is parsed at boot. Once it > is parsed on first use (CONFIG_DEBUG_INFO_BTF_LAZY, later in this > series), it would let any user make the kernel parse it and keep it > parsed until reboot, which is what the option is meant to avoid on > systems that do not use BTF. Any user can do that without this mount. /sys/kernel/btf/vmlinux is 0444. With patch 9 one read() decompresses 5.5 MB into vmalloc_user() memory that is never freed. The parse is the other 2 MB. After the first use the kernel has what every BTF=y kernel has today. There is nothing to guard. > Check the capability first. An unprivileged caller could only ever set > an empty mask; such a no-op delegate option, and a malformed value, > now fail with EPERM as well instead of being accepted or failing with > EINVAL. Privileged callers are not affected. That changes what user space sees, with or without the option. Drop this patch.