From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-61.mta1.migadu.com [95.215.58.61]) (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 6B5331EFFA1 for ; Fri, 28 Aug 2026 09:31:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.61 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787909524; cv=none; b=bcNDm/r6EfowI8QYKlPURvRbPiN6oK3ZoRJ6M1YgNRLQhgDdAXcAs/l+e584hZp4nrZT6byMQQTKHIc8YOSkV1WYFNdvxl/5dRQNhSD2GoqPVqtO87FCAg0Ye5VqJ09KrYcAynA872LkKTxNupBtkR0LHkfFEsRAqDI3GOaQVkE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787909524; c=relaxed/simple; bh=OmlSDs9I0u8FjaIs+dT9chTxqTmmbnf++knS9QEOf3I=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=nh4g8rSrw2T+m3In99QHRCaD0WTSjDFF41n/iagJJhhggmzvn//ZVveO8BbZ4ARIITPkZL/gk+5YEEGX4Uheokk8MpNBt+xhYkSzN6zcVfqP6NRgCkaLycB4wMt4o4teODbWTKsbns8PBbtar0CfCxQoUqDsxw6JcWFkU9FKzjg= 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=B6Y0mpg3; arc=none smtp.client-ip=95.215.58.61 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="B6Y0mpg3" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=OmlSDs9I0u8FjaIs+dT9chTxqTmmbnf++knS9QEOf3I=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787909517; v=1; x=1788514317; b=B6Y0mpg34bMVjcrF4ToIg6+nj9mXhJA02xeVeWwypAF1cAnqamlT2h04NZla4X75HZBXqUww hxmifMN7XtFGCEcVe95cEH32G6ZN8JNGCn879t4B84mYGMVfoSbYlJShIuivIs+JOmroi1AG28B I+/97Otc6r0dPHUguToHAt7A= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 50127a13f27fa597; Fri, 28 Aug 2026 09:31:57 +0000 X-Mizu-Trace-ID: 50127a13f27fa597 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 , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf 1/2] bpf: Fix NULL-ptr-deref when dumping a key-less BTF hash map Date: Fri, 28 Aug 2026 17:31:16 +0800 Message-ID: <20260828093142.179856-1-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 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. That changed once htab and rhtab got a ->map_check_btf to register a dtor: the callback 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) Only array maps have a use for a key-less BTF (DataSec global data). Reject it in htab_map_check_btf() and rhtab_map_check_btf(), restoring the previous behavior, and also let btf_type_show() bail out on a type with no show op instead of dereferencing NULL, so any other path that reaches it with a void type degrades gracefully. 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/btf.c | 4 ++++ kernel/bpf/hashtab.c | 8 ++++++++ 2 files changed, 12 insertions(+) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 91b8ce77f699..3dbbbac4dd2e 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -8248,6 +8248,10 @@ static void btf_type_show(const struct btf *btf, u32 type_id, void *obj, memset(&show->state, 0, sizeof(show->state)); memset(&show->obj, 0, sizeof(show->obj)); + /* A void type (e.g. type_id 0) has no show op, don't deref NULL. */ + if (!t || !btf_type_ops(t)) + return; + btf_type_ops(t)->show(btf, t, type_id, obj, 0, show); } diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index d40cb5dd446c..299859c58b41 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); + /* Unlike array maps, 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); + /* Unlike array maps, 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