bpf: Reject writes for PTR_TO_MAP_KEY in check_helper_mem_access

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>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d953e62b5268d2da5bfe92f014d96786964c87a2..9c1a02b82ecd03465580d44e548d422b817c5c3a 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4861,6 +4861,11 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
                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: