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 tags 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>
---
 kernel/bpf/verifier.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f0ca69f888fa..c7ebddb66385 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10349,10 +10349,27 @@ 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, int func_id)
 {
 	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;
 }
 

-- 
2.43.0

On Sun, 2026-01-18 at 16:16 +0800, Zesen Liu wrote:
> 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 tags 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>
> ---

Note: this patch no longer applies properly because of the change in
      the check_func_proto() signature.

[...]

[...]

> On Jan 20, 2026, at 04:25, Eduard Zingerman <eddyz87@gmail.com> wrote:
> 
> Note: this patch no longer applies properly because of the change in
>      the check_func_proto() signature.

Thanks for pointing this out. I will rebase to bpf-next in v3 to
address the check_func_proto() signature changes.