[PATCH 1/2] bpf: Check if iter args are stack pointers

[Tao Lyu <tao.lyu@xxxxxxx>]

The verifier misses the type checking on iter arguments,
so any pointer types (e.g., map value pointers) can be passed as iter arguments.

We fix this issue by adding a type check to ensure the passed
iter arguments are in the type of PTR_TO_STACK.

Fixes: 06accc8779c1 ("bpf: add support for open-coded iterator loops")
Signed-off-by: Tao Lyu <tao.lyu@xxxxxxx>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 797cf3ed32e0..98afdcecefbc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12234,6 +12234,11 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 					return -EINVAL;
 				}
 			}
+			/* Ensure the iter arg is a stack pointer */
+			if (reg->type != PTR_TO_STACK) {
+				verbose(env, "arg#%d expected pointer to the iterator\n", i);
+				return -EINVAL;
+			}
 			ret = process_iter_arg(env, regno, insn_idx, meta);
 			if (ret < 0)
 				return ret;
-- 
2.34.1