From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-1.mta1.migadu.com [95.215.58.1]) (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 1D501340DA6 for ; Mon, 31 Aug 2026 11:03:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788174211; cv=none; b=OOLY45sgCKHQWMG7a1cEM3Wx9cLmP1SeYa6Gp4cNZg2iaZjQ/IgQAWxtnLToqK1Fvpv3jPa5CPn5pE8WkMx/WV8HsWnJS0Vx+Q4WLnBNUkleKceUxwtHwUMPxflnmDriFyAtXJoozLuTmFEFvRvkD2q9P5oB+uUWWnDK0R52nig= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788174211; c=relaxed/simple; bh=/NN2WxM2riQ1V3asB40Qhut8hxnm4DYXi01Ct2unvcc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=A5Y3t2nuweAx4RIRKWBHtSl1WFAA9dvanK2AXpuuhSUfdLC8MduRXrPYr2x9saH+B8fuacZGibqoDqHOGVc5B5HR71HR3QKX4qT9nlATGO0P5dExbm7YOP4qVyO+nWzdPC2Fu6MAqh+pWMEBjb/462Xnj4ZElhnfpa2gAoCGnSU= 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=ZjEI6aWB; arc=none smtp.client-ip=95.215.58.1 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="ZjEI6aWB" X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=/NN2WxM2riQ1V3asB40Qhut8hxnm4DYXi01Ct2unvcc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788174205; v=1; x=1788779005; b=ZjEI6aWBUKrH0KqAZV9PYhMxsOMeaHfHNh3KAIoHP/E6DG0YeFunLwXEG8yws1q9m95EGMWp Hnq168PdNFnJ9wm5QrGssnsP7Pu/E/b5YCqQbpi4KxdYEzxudpXOcCYy99gMESy1Y4+fnUwQgg6 x2ZKaDntLlEDZxTZwZ2rInkA= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 30aa6c88d071e977; Mon, 31 Aug 2026 11:03:25 +0000 X-Mizu-Trace-ID: 30aa6c88d071e977 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 , Mykyta Yatsenko , Alan Maguire , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf v3 0/5] bpf: Fix NULL-ptr-derefs when showing a void BTF type Date: Mon, 31 Aug 2026 19:01:05 +0800 Message-ID: <20260831110314.150870-1-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This series fixes three NULL-ptr-derefs in BTF handling. Patch 1 handles the syzbot report. A key-less BTF (btf_key_type_id == 0) used to be rejected for hash maps, until htab and rhtab gained a ->map_check_btf (to register a dtor) that does not look at the key, so a key-less hash map is now accepted. Dumping it through bpffs feeds the key type_id 0 into btf_type_seq_show() and NULL-derefs in btf_type_show(). Reject it again. Patches 2 and 3 fix two related, pre-existing crashes reachable via bpf_snprintf_btf(), which renders a type_id taken straight from the BPF program against the vmlinux BTF. A "const void" (a modifier resolving to void) NULL-derefs in btf_modifier_show() - void has no ->show op; a BTF_KIND_VAR NULL-derefs in btf_var_show() - the vmlinux base BTF has no resolved_ids. Patch 2 falls back to btf_df_show(), the "" placeholder already used for FWD/FUNC/FLOAT/DECL_TAG; patch 3 resolves the var's type directly, mirroring the existing guard in btf_modifier_show(). Patches 4 and 5 add selftests for the three cases. They are meant to reproduce the crashes: each deliberately walks the faulting path, so on an unfixed kernel it oopses the task (and panics it under panic_on_oops). That is intentional - the tests verify the fix and reproduce the bug - so a static review flagging them for crashing an unfixed kernel can be ignored. v2 -> v3: Fold in a third fix for the same class of bug, btf_var_show(), reported while reviewing v2. Address review comments (Fixes attribution, verbatim syzbot trace, skip instead of fail). v1 -> v2: AI reported a pre-exist issue. Let's fold it in this series. v2: https://lore.kernel.org/bpf/20260830073242.148092-1-jiayuan.chen@linux.dev/ v1: https://lore.kernel.org/bpf/20260828093142.179856-1-jiayuan.chen@linux.dev/ Jiayuan Chen (5): bpf: Reject key-less BTF for hash maps bpf: Fix NULL-ptr-deref when showing a void BTF type bpf: Fix NULL-ptr-deref in btf_var_show() selftests/bpf: Add test for key-less BTF hash map selftests/bpf: Add test for showing a void BTF type kernel/bpf/btf.c | 20 ++++- kernel/bpf/hashtab.c | 8 ++ .../bpf/prog_tests/btf_map_keyless.c | 82 +++++++++++++++++++ .../selftests/bpf/prog_tests/btf_show_void.c | 81 ++++++++++++++++++ .../selftests/bpf/progs/btf_show_void.c | 24 ++++++ 5 files changed, 213 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_map_keyless.c create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_show_void.c create mode 100644 tools/testing/selftests/bpf/progs/btf_show_void.c -- 2.43.0