[PATCH 5.17 74/75] bpf: Reject writes for PTR_TO_MAP_KEY in check_helper_mem_access

Greg Kroah-Hartman
2022-06-03T18:13:37Z

From: Kumar Kartikeya Dwivedi <memxor@gmail.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@gmail.com>
Link: https://lore.kernel.org/r/20220319080827.73251-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);