linux-kernel - [PATCH 5.17 74/75] bpf: Reject writes for PTR_TO_MAP_KEY in check_helper_mem

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Message-Id: <20220603173823.825178608@linuxfoundation.org>
Date:   Fri,  3 Jun 2022 19:43:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH 5.17 74/75] bpf: Reject writes for PTR_TO_MAP_KEY in check_helper_mem_access

From: Kumar Kartikeya Dwivedi <memxor@...il.com>

commit 7b3552d3f9f6897851fc453b5131a967167e43c2 upstream.

It is not permitted to write to PTR_TO_MAP_KEY, but the current code in
check_helper_mem_access would allow for it, reject this case as well, as
helpers taking ARG_PTR_TO_UNINIT_MEM also take PTR_TO_MAP_KEY.

Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
Link: https://lore.kernel.org/r/20220319080827.73251-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/bpf/verifier.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4832,6 +4832,11 @@ static int check_helper_mem_access(struc
 		return check_packet_access(env, regno, reg->off, access_size,
 					   zero_size_allowed);
 	case PTR_TO_MAP_KEY:
+		if (meta && meta->raw_mode) {
+			verbose(env, "R%d cannot write into %s\n", regno,
+				reg_type_str(env, reg->type));
+			return -EACCES;
+		}
 		return check_mem_region_access(env, regno, reg->off, access_size,
 					       reg->map_ptr->key_size, false);
 	case PTR_TO_MAP_VALUE: