From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-20.mta0.migadu.com [91.218.175.20]) (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 4B7C235F170 for ; Sun, 30 Aug 2026 07:33:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.20 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788075210; cv=none; b=eXgCvEOiJqKZsMBl9/2H/P4XFrtXN7XtQ1zGSRlJa4EmMek574TQP8K9wnWwJeNfkUSyxFwP1wR1LzYJ0sG8+cyJKDGfmtBbrM5LKyQ7h00Da/3WufaHRx/DJGMG2N2lpSJk0f0MCqK7El1AaDOoyhc23gDj4k4xIfR/HC7506g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788075210; c=relaxed/simple; bh=s+hno46646Ftcg4sO1qvoDzrwEmHBxTBKiCcgLmq0KQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mdCOY4wCau3+K71lGLX6oX04/so67L8dpSu5DJDq6FJbppnJrYmoYSY73sAXGDMDFFM21RhQlhXXEhOLyX5M7huBi/kVb0vy4w4AFKZ/JEKjPAOTnz2mBIZKAKajz2SMGr6uSPzM6WDdFKInwFL7HWAqC47C1T9AkLF3Tp2gWH4= 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=vD21z1mF; arc=none smtp.client-ip=91.218.175.20 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="vD21z1mF" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=s+hno46646Ftcg4sO1qvoDzrwEmHBxTBKiCcgLmq0KQ=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788075205; v=1; x=1788680005; b=vD21z1mFauS+Lrxnd+BySCazay2IwmLwVSxLQWEC3H21SavkHgTM3X0Ze2mIEmZUL9bDffwQ sKZbC28QZMmHAyz/QQTdBlBAq1rcxKh7y2T730uGbKJcQpnwJW7JwVZjtdu9+qMqHKC4hBUV7Xe 79TGXGDTBYTGEHgvObJA83Gc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id db3a522f16ad53d8; Sun, 30 Aug 2026 07:33:25 +0000 X-Mizu-Trace-ID: db3a522f16ad53d8 X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , syzbot+37b56485bbbf90ad8489@syzkaller.appspotmail.com, 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 v2 1/4] bpf: Reject key-less BTF for hash maps Date: Sun, 30 Aug 2026 15:30:56 +0800 Message-ID: <20260830073242.148092-2-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260830073242.148092-1-jiayuan.chen@linux.dev> References: <20260830073242.148092-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit map_check_btf() allows a key-less BTF (btf_key_type_id == 0) only for maps that have a ->map_check_btf callback, and leaves the actual decision to that callback. Hash maps used to have no ->map_check_btf, so a key-less BTF was rejected outright. Since commit 1df97a7453ee ("bpf: Register dtor for freeing special fields") htab and rhtab got a ->map_check_btf to register a dtor, but it does not look at the key, so a key-less hash map now passes map_check_btf() and gets created. Reading it back through bpffs then feeds the key type_id 0 into btf_type_seq_show(); btf_type_by_id() returns the void type, kind_ops[BTF_KIND_UNKN] is NULL, and btf_type_show() dereferences it: KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] RIP: 0010:btf_type_show (kernel/bpf/btf.c:8251) Call Trace: btf_type_seq_show_flags (kernel/bpf/btf.c:8269) btf_type_seq_show (kernel/bpf/btf.c:8277) htab_map_seq_show_elem (kernel/bpf/hashtab.c:1669) map_seq_show (kernel/bpf/inode.c:293) seq_read_iter (fs/seq_file.c:273) seq_read (fs/seq_file.c:163) vfs_read (fs/read_write.c:572) ksys_read (fs/read_write.c:716) __x64_sys_read (fs/read_write.c:725) do_syscall_64 (arch/x86/entry/syscall_64.c:61) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Reject a key-less BTF in htab_map_check_btf() and rhtab_map_check_btf(), restoring the previous behavior. Fixes: 1df97a7453ee ("bpf: Register dtor for freeing special fields") Fixes: 6905f8601298 ("bpf: Allow special fields in resizable hashtab") Reported-by: syzbot+37b56485bbbf90ad8489@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6a8f4e88.27659fcc.2ceef7.0008.GAE@google.com/T/ Signed-off-by: Jiayuan Chen --- kernel/bpf/hashtab.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index d40cb5dd446c..43123424183c 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -530,6 +530,10 @@ static int htab_map_check_btf(struct bpf_map *map, const struct btf *btf, { struct bpf_htab *htab = container_of(map, struct bpf_htab, map); + /* Hash maps have no use for a key-less BTF. */ + if (btf_type_is_void(key_type)) + return -EINVAL; + if (htab_is_prealloc(htab)) return 0; /* @@ -3110,6 +3114,10 @@ static int rhtab_map_check_btf(struct bpf_map *map, const struct btf *btf, { struct bpf_rhtab *rhtab = container_of(map, struct bpf_rhtab, map); + /* Hash maps have no use for a key-less BTF. */ + if (btf_type_is_void(key_type)) + return -EINVAL; + return bpf_ma_set_dtor(map, &rhtab->ma, rhtab_mem_dtor); } -- 2.43.0