From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D9C72ED843; Tue, 25 Aug 2026 14:01:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787666471; cv=none; b=ACKemumSleluAsn8LEj6EhzP1Dg4r+lKtVu89ERRu4Hf3gQcRG4/eTIE+ovBWaGuGSVDCDDxjUeMjVrgLCPsZifHFHKs2Zv8uSxgpwm4e6RV3l5J5YM+2lCLhvdWPOnP1FhFjTofxWKqvtAHdyRBnCyLHw6sGfDgQXo7raBtrAY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787666471; c=relaxed/simple; bh=cIhaELCkW8cfVRnh4uvQ4oBWDPA31Z/vgU8z2GBGoIE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nDa8Nfk3IAPKDIQV39cC9gRU1yuYMhiemSjHq4biU5Yk+QhdBAxz1KLyNnSJt6aXK00s6HMJ3/s2N/kCerE5oEfbPDaVeL0Xh9i+fh9Xf84fyeBqJwz6jqxDejX6/HXEdRfqYkbo/FYzieRV+iZNaEk1z5i81Fagq8iuQxbyG+o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=je+xljRl; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="je+xljRl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB6BF1F000E9; Tue, 25 Aug 2026 14:01:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787666470; bh=ldUPWWzOaci0axnN7L2QLpmUmzGtlXrL9RUc/AIU0M8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=je+xljRlWxpsHtKAHR2kCwNbVf2YHe16ppt+DNsSAJ4sc5FyX5DBuYkiXBdx/Ekoo Iy4EAMjahpFg1x2+yUEWpY5UNRyuvIWNm6+6bvJahsOE4EugxKURGNHm6+KF7S7Fwg F0EQtr5wx4MvTHP+2vp2a9YTFw+qNzPFuaZ+lJUw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Xiang Mei , Weiming Shi , Emil Tsalapatis , Paul Chaignon , Alexei Starovoitov , Andrey Troshin Subject: [PATCH 5.10 52/57] bpf: reject negative CO-RE accessor indices in bpf_core_parse_spec() Date: Tue, 25 Aug 2026 15:27:14 +0200 Message-ID: <20260825132543.378695177@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260825132541.342390421@linuxfoundation.org> References: <20260825132541.342390421@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Weiming Shi commit 1c22483a2c4bbf747787f328392ca3e68619c4dc upstream. CO-RE accessor strings are colon-separated indices that describe a path from a root BTF type to a target field, e.g. "0:1:2" walks through nested struct members. bpf_core_parse_spec() parses each component with sscanf("%d"), so negative values like -1 are silently accepted. The subsequent bounds checks (access_idx >= btf_vlen(t)) only guard the upper bound and always pass for negative values because C integer promotion converts the __u16 btf_vlen result to int, making the comparison (int)(-1) >= (int)(N) false for any positive N. When -1 reaches btf_member_bit_offset() it gets cast to u32 0xffffffff, producing an out-of-bounds read far past the members array. A crafted BPF program with a negative CO-RE accessor on any struct that exists in vmlinux BTF (e.g. task_struct) crashes the kernel deterministically during BPF_PROG_LOAD on any system with CONFIG_DEBUG_INFO_BTF=y (default on major distributions). The bug is reachable with CAP_BPF: BUG: unable to handle page fault for address: ffffed11818b6626 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Oops: Oops: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 85 Comm: poc Not tainted 7.0.0-rc6 #18 PREEMPT(full) RIP: 0010:bpf_core_parse_spec (tools/lib/bpf/relo_core.c:354) RAX: 00000000ffffffff Call Trace: bpf_core_calc_relo_insn (tools/lib/bpf/relo_core.c:1321) bpf_core_apply (kernel/bpf/btf.c:9507) check_core_relo (kernel/bpf/verifier.c:19475) bpf_check (kernel/bpf/verifier.c:26031) bpf_prog_load (kernel/bpf/syscall.c:3089) __sys_bpf (kernel/bpf/syscall.c:6228) CO-RE accessor indices are inherently non-negative (struct member index, array element index, or enumerator index), so reject them immediately after parsing. Fixes: ddc7c3042614 ("libbpf: implement BPF CO-RE offset relocation algorithm") Reported-by: Xiang Mei Signed-off-by: Weiming Shi Reviewed-by: Emil Tsalapatis Acked-by: Paul Chaignon Link: https://lore.kernel.org/r/20260404161221.961828-2-bestswngs@gmail.com Signed-off-by: Alexei Starovoitov [Andrey Troshin: backport fixs from tools/lib/bpf/relo_core.c to tools/lib/bpf/libbpf.c] Signed-off-by: Andrey Troshin Signed-off-by: Greg Kroah-Hartman --- tools/lib/bpf/libbpf.c | 2 ++ 1 file changed, 2 insertions(+) --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -4554,6 +4554,8 @@ static int bpf_core_parse_spec(const str ++spec_str; if (sscanf(spec_str, "%d%n", &access_idx, &parsed_len) != 1) return -EINVAL; + if (access_idx < 0) + return -EINVAL; if (spec->raw_len == BPF_CORE_SPEC_MAX_LEN) return -E2BIG; spec_str += parsed_len;