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 DC9293E95A4; Wed, 20 May 2026 18:02:43 +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=1779300165; cv=none; b=LRkS7juU7Etb04C2UmmH0C/2s/Ae6QnNvQ+FiIv5afmeRi9Dlcnx8LBdB31cIjbOzNctUf8wwXJqoD2R1DP5BflGg91p9SU2bKg/vSOey0t8PoKd+nwyFDoAEGm6unPp86uey7WO1XXv+KrWpCIFZ/pb8hB7WFlh91djeGVmc90= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779300165; c=relaxed/simple; bh=+1JcpVOCHXMQMtPSjAaZF1JopU+KR/vU9iWfKtBWuuQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gySG7URItGE52eObdWt/W6YRU5vTmYV1pqAPOe5pYGYKsYeCvuQC0OM6IXabyOqk2M/nc2WALf4vuBPGDtYuaHQXjnP37YmqWl4hEQsSqUzzKVYPECEwwK4Q3GscSKvsO13yHtYcaIY+bkbrWRhRh+PsrcSPpVW7frID7P3kgs4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jZMigbus; 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="jZMigbus" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50A121F00898; Wed, 20 May 2026 18:02:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779300163; bh=BeWGe/6HJJwi9Yq2KJX+9Y+vWZu7i/DcUV74G4Typag=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=jZMigbusIxpFD6BlnWHHdHP2KPoRzzSFPJ+aGVj/zb5giTp7e1hYxFwm8uMQ+r2/b CefiIAoqyZEv6Ug6lDuizKT+1gVlXQps5R76l05aGPKmtUgo5QhHOk2NNXyX43EhAH H6FXNrAzxHrtneBBjc3yCbANTTsNOTygU92N90IY= 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 , Sasha Levin Subject: [PATCH 6.12 069/666] bpf: reject negative CO-RE accessor indices in bpf_core_parse_spec() Date: Wed, 20 May 2026 18:14:40 +0200 Message-ID: <20260520162112.726835876@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162111.222830634@linuxfoundation.org> References: <20260520162111.222830634@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Weiming Shi [ Upstream commit 1c22483a2c4bbf747787f328392ca3e68619c4dc ] 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 Signed-off-by: Sasha Levin --- tools/lib/bpf/relo_core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c index 63a4d5ad12d1a..04c8febfc0aa7 100644 --- a/tools/lib/bpf/relo_core.c +++ b/tools/lib/bpf/relo_core.c @@ -293,6 +293,8 @@ int bpf_core_parse_spec(const char *prog_name, const struct btf *btf, ++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; -- 2.53.0