[PATCH bpf-next v2 5/7] bpf: Fix check_reg_type for PTR_TO_BTF_ID

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

The current code does type matching for the case where reg->type is
PTR_TO_BTF_ID or has the PTR_TRUSTED flag. However, this only needs to
occur for non-MEM_ALLOC and non-MEM_PERCPU cases, but will include both
as per the current code.

The MEM_ALLOC case with or without PTR_TRUSTED needs to be handled
specially by the code for type_is_alloc case, while MEM_PERCPU case must
be ignored. Hence, to restore correct behavior and for clarity,
explicitly list out the handled PTR_TO_BTF_ID types which should be
handled for each case using a switch statement.

Helpers currently only take:
	PTR_TO_BTF_ID
	PTR_TO_BTF_ID | PTR_TRUSTED
	PTR_TO_BTF_ID | MEM_RCU
	PTR_TO_BTF_ID | MEM_ALLOC
	PTR_TO_BTF_ID | MEM_PERCPU
	PTR_TO_BTF_ID | MEM_PERCPU | PTR_TRUSTED

This fix was also described (for the MEM_ALLOC case) in [0].

  [0]: https://lore.kernel.org/bpf/20221121160657.h6z7xuvedybp5y7s@apollo

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6837657b46bf..8dbd20735e92 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6522,7 +6522,14 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	return -EACCES;
 
 found:
-	if (reg->type == PTR_TO_BTF_ID || reg->type & PTR_TRUSTED) {
+	if (base_type(reg->type) != PTR_TO_BTF_ID)
+		return 0;
+
+	switch ((int)reg->type) {
+	case PTR_TO_BTF_ID:
+	case PTR_TO_BTF_ID | PTR_TRUSTED:
+	case PTR_TO_BTF_ID | MEM_RCU:
+	{
 		/* For bpf_sk_release, it needs to match against first member
 		 * 'struct sock_common', hence make an exception for it. This
 		 * allows bpf_sk_release to work for multiple socket types.
@@ -6558,13 +6565,23 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 				return -EACCES;
 			}
 		}
-	} else if (type_is_alloc(reg->type)) {
+		break;
+	}
+	case PTR_TO_BTF_ID | MEM_ALLOC:
 		if (meta->func_id != BPF_FUNC_spin_lock && meta->func_id != BPF_FUNC_spin_unlock) {
 			verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n");
 			return -EFAULT;
 		}
+		/* Handled by helper specific checks */
+		break;
+	case PTR_TO_BTF_ID | MEM_PERCPU:
+	case PTR_TO_BTF_ID | MEM_PERCPU | PTR_TRUSTED:
+		/* Handled by helper specific checks */
+		break;
+	default:
+		verbose(env, "verifier internal error: invalid PTR_TO_BTF_ID register for type match\n");
+		return -EFAULT;
 	}
-
 	return 0;
 }
 
-- 
2.39.2