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Thu, 29 Oct 2026 09:33:57 -0700 (PDT) Received: from localhost ([153.61.198.253]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb361f392esm107005ad.3.2026.10.29.09.33.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Oct 2026 09:33:57 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Thu, 29 Oct 2026 16:33:56 +0000 Message-Id: Subject: Re: [PATCH bpf] libbpf: Reject excessive program counts in generated loaders From: "Alexei Starovoitov" To: "Mahe Tardy" , Cc: "Andrii Nakryiko" , "Eduard Zingerman" , "Ihor Solodrai" , "Daniel Borkmann" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , , "John Fastabend" In-Reply-To: <20261028183947.9606-1-mahe.tardy@gmail.com> References: <20261028183947.9606-1-mahe.tardy@gmail.com> Content-Transfer-Encoding: 8bit X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Wed, Oct 28, 2026 at 11:39 AM Mahe Tardy wrote: > @@ -122,6 +122,11 @@ void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps > + if (nr_progs > MAX_USED_PROGS) { > + pr_warn("Total programs exceeds %d\n", MAX_USED_PROGS); > + gen->error = -E2BIG; > + return; > + } nr_progs is obj->nr_programs. It counts subprogs and progs with autoload == false too. See commit 259172bb6514 ("libbpf: Fix gen_loader assumption on number of programs."). Only a prog that reaches bpf_gen__prog_load() takes a slot in prog_fd[]. Two objects with obj->nr_programs == 33: object today this patch should be ------------------- --------------- ------------- ------------- 33 progs -EACCES at load -E2BIG at gen -E2BIG at gen 1 prog, 32 subprogs -EACCES at load -E2BIG at gen loads The second object fails today because of the cleanup loop in bpf_gen__init(). It closes nr_progs slots of prog_fd[], and prog_fd[32] is at r10 + 0: r1 = *(u32 *)(r10 +0) invalid read from stack R10 off=0 size=4 Lets fix both: clamp the loop and check the limit where a prog takes the slot, like add_map_fd() does. Something like this (not even compile tested): diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c --- a/tools/lib/bpf/gen_loader.c +++ b/tools/lib/bpf/gen_loader.c @@ -139,6 +139,8 @@ void bpf_gen__init(struct bpf_gen *gen, int log_level, int nr_progs, int nr_maps emit(gen, BPF_MOV64_IMM(BPF_REG_3, 0)); emit(gen, BPF_EMIT_CALL(BPF_FUNC_probe_read_kernel)); + /* nr_progs includes subprogs and progs that are not loaded */ + nr_progs = min(nr_progs, MAX_USED_PROGS); /* amount of stack actually used, only used to calculate iterations, not stack offset */ nr_progs_sz = offsetof(struct loader_stack, prog_fd[nr_progs]); /* jump over cleanup code */ @@ -1134,6 +1136,11 @@ void bpf_gen__prog_load(struct bpf_gen *gen, gen->attach_kind = 0; } emit_check_err(gen); + if (gen->nr_progs == MAX_USED_PROGS) { + pr_warn("Total programs exceeds %d\n", MAX_USED_PROGS); + gen->error = -E2BIG; + return; + } /* remember prog_fd in the stack, if successful */ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_7, stack_off(prog_fd[gen->nr_progs]))); since it was already applied. pls send a follow up.