From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-200.mta0.migadu.com [91.218.175.200]) (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 E452B26E165 for ; Tue, 1 Sep 2026 10:50:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788259804; cv=none; b=GizIss+YiKKB5OZMYvHMex+fnUtnjyDt2G0TSoVEkuIVsoCV6PNn+bkoK8mRdTGwtzp7BES9necQxHBzl31ZzLNZCS/gg13Bty/gIk8h/1TRjZirxWRI8JfaizSoSCEM+D7UdHL9k1VES55CRbLBMp2d0oG6cSIGe8xp/DcILJs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788259804; c=relaxed/simple; bh=e4A14JjhkHMHsrE/lM9IyERxAQ8ySs6n2okyUEeUz/A=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=e2JWMcT5/D+TYGC/DbWmt9feS6I7jC6kcr3+NG4CqObed8mzXNQffpS4Kp2bQS7ta2grVvhsOhkXqRZfzofluHf8Fa4S8DOj0ayhfBkD+pno5H3lHI3I7ixpTV8x+nv3Rs45fCeHjXZbGc8eeVjtd4Z2g88peOLES+H9Lt55TRc= 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=gi8f+0Ze; arc=none smtp.client-ip=91.218.175.200 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="gi8f+0Ze" X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=e4A14JjhkHMHsrE/lM9IyERxAQ8ySs6n2okyUEeUz/A=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788259799; v=1; x=1788864599; b=gi8f+0ZemH4t0zsoKHdxKfA7nniTRlbPFOXpI4l06+UT6iqm+GaaQRRfBy7D4uZIJypJfX92 N1KJFgP/QJenpHuLQpFY7kMJIlTlks15brvHO0okLsgjnfggNlgKk1sFkHc+IMQnKjb8IGMalSC 47RuXasAYlT/sutY8ZQvjhLY= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 4b111e7144bc5b32; Tue, 01 Sep 2026 10:49:59 +0000 X-Mizu-Trace-ID: 4b111e7144bc5b32 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 v4 0/5] bpf: Fix NULL-ptr-derefs when showing a void BTF type Date: Tue, 1 Sep 2026 18:47:34 +0800 Message-ID: <20260901104924.346187-1-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. Patch 4 checks a key-less hash and rhash map is rejected at creation. Patch 5 extends the snprintf_btf test to render a "const void" and a BTF_KIND_VAR from the vmlinux BTF and checks they resolve without crashing. v3 -> v4: Drop the pin-and-read reproducer from the key-less map test, fold the void/VAR test into the existing snprintf_btf test, and simplify patch 2's wording (review comments). 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. v3: https://lore.kernel.org/bpf/20260831110314.150870-1-jiayuan.chen@linux.dev/ 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 | 19 ++++- kernel/bpf/hashtab.c | 6 ++ .../bpf/prog_tests/btf_map_keyless.c | 59 ++++++++++++++ .../selftests/bpf/prog_tests/snprintf_btf.c | 79 +++++++++++++++++++ .../selftests/bpf/progs/snprintf_btf_void.c | 24 ++++++ 5 files changed, 185 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_map_keyless.c create mode 100644 tools/testing/selftests/bpf/progs/snprintf_btf_void.c -- 2.43.0