From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-214.mta0.migadu.com [91.218.175.214]) (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 F2A3847DD74 for ; Tue, 1 Sep 2026 10:50:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.214 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788259828; cv=none; b=hW4EWeGhyl4GkfcUI3FpoFn6NGYMv0rdb8hmEhx9Uy6V625STG6wekM2RO+dNlf9jLQDgjscBKX/392r7VL68W40mkLlwjNWcsmKPN7IzDfkniKnn+oME/27T6Yjn16eFst+8iVsF7DBExIAiuRLeBtbnQEFguh8z4mAh0Kt/jU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788259828; c=relaxed/simple; bh=C1F/at+ZpcyorQfJWG9U8cQlYWLtImAZlUOYJDjZBzI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Iti0nIfn9VFCRwtp9rrHKwEhYo1jCR2ialOjNSCdN7OrRA0TOBBjU8oixMmfIpEUmKrM8rrdwbbjWhNOuCSl8M3vl5wLdItx1SoMzPXGAZ/4I1zEL9DegR5cGZ0zBvBHw32bF+2rzIpucYYX1QBxdixU4MfpY0pMG6JcNwDe6Jc= 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=HHuF9GYy; arc=none smtp.client-ip=91.218.175.214 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="HHuF9GYy" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=C1F/at+ZpcyorQfJWG9U8cQlYWLtImAZlUOYJDjZBzI=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788259825; v=1; x=1788864625; b=HHuF9GYyS4WSoVgIehCZYROVFwhQ0t5ZviCBNC6SjLVpoJfKPwlmsoa3eY+ivE//k8ZwUkXR t5/n6LO92oK1/zR1h9BuNCGJnXpbcnrtbx3cR+BBWRXaKrVh/8s09EUFHrBQQIOjmDkDqlux7pX GEHDKn61y1HH6QfnrbLWIHRc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id d642d75bbf501021; Tue, 01 Sep 2026 10:50:24 +0000 X-Mizu-Trace-ID: d642d75bbf501021 X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , syzbot+37b56485bbbf90ad8489@syzkaller.appspotmail.com, Ihor Solodrai , 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 Subject: [PATCH bpf v4 1/5] bpf: Reject key-less BTF for hash maps Date: Tue, 1 Sep 2026 18:47:35 +0800 Message-ID: <20260901104924.346187-2-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260901104924.346187-1-jiayuan.chen@linux.dev> References: <20260901104924.346187-1-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. 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: RIP: 0010:btf_type_show+0x223/0x2e0 kernel/bpf/btf.c:8232 RSP: 0018:ffffc9000399f868 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000028 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 R10: ffffc9000399f970 R11: 0000000000000001 R12: ffffffff9b96b140 R13: ffffc9000399f8e0 R14: ffff88803d393c00 R15: 0000000000000003 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000000 CR3: 000000003d213000 CR4: 0000000000352ef0 DR0: 0000000039ae8f55 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 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 traverse.part.0.constprop.0+0x107/0x650 fs/seq_file.c:112 traverse fs/seq_file.c:99 [inline] 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 ksys_pread64 fs/read_write.c:764 [inline] __do_sys_pread64 fs/read_write.c:772 [inline] __se_sys_pread64 fs/read_write.c:769 [inline] __x64_sys_pread64+0x1eb/0x250 fs/read_write.c:769 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] 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 Acked-by: Ihor Solodrai --- kernel/bpf/hashtab.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index d40cb5dd446c..7f55d6421e72 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -530,6 +530,9 @@ 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); + if (btf_type_is_void(key_type)) + return -EINVAL; + if (htab_is_prealloc(htab)) return 0; /* @@ -3110,6 +3113,9 @@ 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); + if (btf_type_is_void(key_type)) + return -EINVAL; + return bpf_ma_set_dtor(map, &rhtab->ma, rhtab_mem_dtor); } -- 2.43.0