From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-106.mta0.migadu.com [91.218.175.106]) (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 A3EAE3815E3 for ; Mon, 31 Aug 2026 21:01:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.106 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788210086; cv=none; b=RkYzRhb+0saqQTPBodMUx3vAi6BZqacmP0EkdZn5L2V7we0Za2hgLl1WZ0i28FQD4P5/xwFO3gXdZMT3G6wugcEgSoivzATpC3rTpyo9J5SUAHrruQ4mzVydB1AmeyUcMrJrl3Pt/UVvV9e8K5WuHWV/sxId6loJAEnKNM1ml3I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788210086; c=relaxed/simple; bh=GWmCf+O61tAOQqtKY80TtsOd0RzoToenooRbBEaWh10=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Yrp94ekKyCV+R4jayOgzTOj2bf2JxY4OtxswUGjiNRew8G38NBPCpfuhY9O1DnEYXpafCRelPoXOLbUMq5jAAKiNOyHEVNqcqaEkU8YCCPC8ISlCV+CAXv4b+DEpTuFHd+0XmFaUMYcpFQ+QnqkuYPA3UvzN86VMjouAX/1C84s= 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=K4bU5rPm; arc=none smtp.client-ip=91.218.175.106 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="K4bU5rPm" X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=GWmCf+O61tAOQqtKY80TtsOd0RzoToenooRbBEaWh10=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788210082; v=1; x=1788814882; b=K4bU5rPmVZvAK0VoQ8lFevM/E0qpJ7lWAK6myjYCBGzhisJcj33Ez/3lG//g7e7KgL5X13vo T0fdCBlC8dS8r/f62UbuACRGAubjCdVVt09grDbc3jkCmwD50e9P1X8a+NLvyVQAMdEs1CjMriK yL0/dYjIPMhHLYBYhV6X+5xU= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id cf44543441aa24a4; Mon, 31 Aug 2026 21:01:22 +0000 X-Mizu-Trace-ID: cf44543441aa24a4 X-Migadu-Flow: FLOW_OUT Message-ID: <1896f171-ec63-48f2-9ef8-cb82d52f2c25@linux.dev> Date: Mon, 31 Aug 2026 14:01:12 -0700 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf v3 1/5] bpf: Reject key-less BTF for hash maps To: Jiayuan Chen , bpf@vger.kernel.org Cc: 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 , Shuah Khan , Mykyta Yatsenko , Alan Maguire , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260831110314.150870-1-jiayuan.chen@linux.dev> <20260831110314.150870-2-jiayuan.chen@linux.dev> Content-Language: en-US From: Ihor Solodrai In-Reply-To: <20260831110314.150870-2-jiayuan.chen@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/31/26 4:01 AM, Jiayuan Chen wrote: > 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 when htab and rhtab gained a ->map_check_btf to register a > dtor - htab in commit 1df97a7453ee ("bpf: Register dtor for freeing > special fields") and rhtab in commit 6905f8601298 ("bpf: Allow special > fields in resizable hashtab"). Neither looks at the key, so a key-less > hash map now passes map_check_btf() and gets created. Reading it back > through bpffs 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+0x223/0x2e0 kernel/bpf/btf.c:8232 > Call Trace: > > btf_type_seq_show_flags+0xca/0x120 kernel/bpf/btf.c:8250 > htab_map_seq_show_elem+0x12e/0x350 kernel/bpf/hashtab.c:1669 > map_seq_show+0x13d/0x1e0 kernel/bpf/inode.c:293 > seq_read_iter+0x93f/0x1270 fs/seq_file.c:196 > seq_read+0x344/0x4d0 fs/seq_file.c:163 > vfs_read+0x1e4/0xb40 fs/read_write.c:572 > __x64_sys_pread64+0x1eb/0x250 fs/read_write.c:769 > do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > 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. */ nit: I think this comment is unnecessary in both places. Other than that the fix makes sense to me, thanks. Acked-by: Ihor Solodrai > + 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); > } >