bpf: Require ARG_PTR_TO_MEM with memory flag

Add check to ensure that ARG_PTR_TO_MEM is used with either MEM_WRITE or
MEM_RDONLY.

Using ARG_PTR_TO_MEM alone without flags does not make sense because:

- If the helper does not change the argument, missing MEM_RDONLY causes the
verifier to incorrectly reject a read-only buffer.
- If the helper does change the argument, missing MEM_WRITE causes the
verifier to incorrectly assume the memory is unchanged, leading to errors
in code optimization.

Co-developed-by: Shuran Liu <electronlsr@gmail.com>
Signed-off-by: Shuran Liu <electronlsr@gmail.com>
Co-developed-by: Peili Gao <gplhust955@gmail.com>
Signed-off-by: Peili Gao <gplhust955@gmail.com>
Co-developed-by: Haoran Ni <haoran.ni.cs@gmail.com>
Signed-off-by: Haoran Ni <haoran.ni.cs@gmail.com>
Signed-off-by: Zesen Liu <ftyghome@gmail.com>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260120-helper_proto-v3-2-27b0180b4e77@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f11dc5366e5b49cf8506fc738ec258607a896760..bca0ca82d164b5661f3623e278d20ad8b521cc29 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10441,10 +10441,27 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
        return true;
 }
 
+static bool check_mem_arg_rw_flag_ok(const struct bpf_func_proto *fn)
+{
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
+               enum bpf_arg_type arg_type = fn->arg_type[i];
+
+               if (base_type(arg_type) != ARG_PTR_TO_MEM)
+                       continue;
+               if (!(arg_type & (MEM_WRITE | MEM_RDONLY)))
+                       return false;
+       }
+
+       return true;
+}
+
 static int check_func_proto(const struct bpf_func_proto *fn)
 {
        return check_raw_mode_ok(fn) &&
               check_arg_pair_ok(fn) &&
+              check_mem_arg_rw_flag_ok(fn) &&
               check_btf_id_ok(fn) ? 0 : -EINVAL;
 }