From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-98.mta0.migadu.com [91.218.175.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F954480965 for ; Thu, 10 Sep 2026 12:23:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789043022; cv=none; b=Uaax+VEW4dt9hkK7jg69Rz0GjTfYGukFT58cZYF4+7gNxkOpcr0hg9ioO3YmDQM/H+YXzNbdDUBgoWek3n5HJaWWO2yT0+jYRDz4lsDWQ+7cqpxN7WnshzYWFTTXpzCrToq9XbQi8Nm2VE3aY7rMkYOO9Rcj2NLthNluim+mJnU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789043022; c=relaxed/simple; bh=57KixXK0jLSgxLPsjVJJCKlr3Q1akw4Iat31BLzPYuE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=CvqI/m5J9ZehYv577PH/u2haFK45pCc611rrv5t9B1YWriJDTZoiTxOe332UGnwwL3V8sHg0msxab0OtjMDIzQpxE2GM5kRu38Vd3IpY1pYzNoflrgp3PRBhq4as9k46/EAkKCXVTytwZOQWSE7laLlnEleXmGGq+eZjrbdENl0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=o3DO2PhD; arc=none smtp.client-ip=91.218.175.98 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="o3DO2PhD" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=57KixXK0jLSgxLPsjVJJCKlr3Q1akw4Iat31BLzPYuE=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789043018; v=1; x=1789647818; b=o3DO2PhDZ6Kh9v/HJYDlhPS6whwkfw7fAQdRWzfvTMjPqsUlWCFakEZnfmMCBkZntxg0kRxB uVQLbJF44zD8hkYe2uMKpZU75wrFR1d4p7fuZbZN0Y76/an5z52twx0tnujVmAGoHb5GaYVZtxD V9NKlKKwSr8+4k+tyl29nhD8= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id dc779369e26ad385; Thu, 10 Sep 2026 12:23:38 +0000 X-Mizu-Trace-ID: dc779369e26ad385 X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , Amery Hung , Tejun Heo , Matt Bobrowski , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf 1/2] bpf: Fix divide-by-zero in btf_struct_walk() Date: Thu, 10 Sep 2026 20:22:55 +0800 Message-ID: <20260910122316.186384-1-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When an access goes past the struct and the last member is a flexible array, btf_struct_walk() folds the offset back into a single element with (off - moff) % t->size, but never checks that the element type has a size. BTF takes an empty struct, so this in program BTF /* event could be empty */ struct event { #ifdef HAVE_TIMESTAMP __u64 ts; #endif }; struct batch { int nr; struct event events[]; }; divides by zero at prog load time. Getting there needs a PTR_TO_BTF_ID that is not MEM_ALLOC, e.g. a plain read of a local kptr stashed in a map from a sleepable program. Oops: divide error: 0000 [#1] SMP KASAN PTI RIP: 0010:btf_struct_walk+0x53f/0x1570 Call Trace: btf_struct_access+0x42a/0xcd0 check_ptr_to_btf_access+0x4dc/0x1160 check_mem_access+0x3a45/0x8740 check_load_mem+0x36a/0xd10 do_check_common+0x3ef0/0xb210 bpf_check+0x6d3b/0x8580 bpf_prog_load+0xf7c/0x2720 __sys_bpf+0xa83/0x3690 __x64_sys_bpf+0xc7/0x150 x64_sys_call+0x1f3f/0x27e0 do_syscall_64+0xe5/0x610 entry_SYSCALL_64_after_hwframe+0x76/0x7e Reject a zero-sized element type. The fixed array path in the same function already bails out on the same thing: btf_struct_walk() ... /* skip empty array */ if (moff == mtrue_end) continue; msize /= total_nelems; Fixes: 9c5f8a1008a1 ("bpf: Support variable length array in tracing programs") Signed-off-by: Jiayuan Chen --- kernel/bpf/btf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 31057c8f3a7c..1c5de50b9cab 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -7203,7 +7203,7 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf, if (btf_type_is_int(t)) return WALK_SCALAR; - if (!btf_type_is_struct(t)) + if (!btf_type_is_struct(t) || !t->size) goto error; off = (off - moff) % t->size; -- 2.43.0