From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-13.mta1.migadu.com [95.215.58.13]) (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 3DC3C342509 for ; Mon, 31 Aug 2026 11:03:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788174237; cv=none; b=aYoEaFQb1RmPT32m+epnFNcKJWF0ECirGaNXKCDBrE8ws/GpzXXUTRwyNyN8qx6Ks+aumfFSy9U4WfSUqTQfuGUEgI4pkGcjvZf6imCB/UOjjHjN73O7tpZaOZJJSGmPbPE8lkl2HLQXipSVQDO8wBGll4bU+CstH/M96Rb1XNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788174237; c=relaxed/simple; bh=ChU7rLrz5Ly5f6u8c+cGt26nIjegz2kM1bSEHnszRUA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oycDnOjVFbpD3MEh/6tEHPAnW7I5C5zqQT5x9KC6uZleIk9gwhpL1IxmgkUY/FL0PbYh6YbEHFpUhw1GSgxVdj8ex6q/e0Bxn55wXx9pcQOE5OZi6rBgOK4hSdDFshJ8hxjWsXG/BZOttDhXKM0qmUk6isce1bYRNf7SG7fmklk= 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=jmwFNBib; arc=none smtp.client-ip=95.215.58.13 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="jmwFNBib" X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=ChU7rLrz5Ly5f6u8c+cGt26nIjegz2kM1bSEHnszRUA=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788174234; v=1; x=1788779034; b=jmwFNBibWAk20ARxYY5i/Yk8K8RAIQPX/aRb+6F9DgC4ddC+HGw6D85H9hQIgS5KZcTaQ/BH PCPU62Nghsr/aTvAKVTTZqMSrd++WNzlnxDVUo+0BfvITOSDc1q3YsK2MqAsXBXuq/I4CcN2Iwu t2EvpIrr7GJyTg2uKyHqFRCw= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 27ca0f8a3d15d337; Mon, 31 Aug 2026 11:03:53 +0000 X-Mizu-Trace-ID: 27ca0f8a3d15d337 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 v3 1/5] bpf: Reject key-less BTF for hash maps Date: Mon, 31 Aug 2026 19:01:06 +0800 Message-ID: <20260831110314.150870-2-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260831110314.150870-1-jiayuan.chen@linux.dev> References: <20260831110314.150870-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@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 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. */ + 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