[PATCH bpf 1/2 v2] bpf: Fix wrong reg type conversion in release_reference()

[Youlin Li <liulin063@gmail.com>]

Some helper functions will allocate memory. To avoid memory leaks, the
verifier requires the eBPF program to release these memories by calling
the corresponding helper functions.

When a resource is released, all pointer registers corresponding to the
resource should be invalidated. The verifier use release_references() to
do this job, by apply  __mark_reg_unknown() to each relevant register.

It will give these registers the type of SCALAR_VALUE. A register that
will contain a pointer value at runtime, but of type SCALAR_VALUE, which
may allow the unprivileged user to get a kernel pointer by storing this
register into a map.

Using __mark_reg_not_init() while NOT allow_ptr_leaks can mitigate this
problem.

Fixes: fd978bf7fd31 ("bpf: Add reference tracking to verifier")
Signed-off-by: Youlin Li <liulin063@gmail.com>
---
v1->v2: Use __mark_reg_not_init() only when !allow_ptr_leaks.

 kernel/bpf/verifier.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9ab7188d8f68..1bb797bf9bbc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6618,8 +6618,12 @@ static int release_reference(struct bpf_verifier_env *env,
 		return err;
 
 	bpf_for_each_reg_in_vstate(env->cur_state, state, reg, ({
-		if (reg->ref_obj_id == ref_obj_id)
-			__mark_reg_unknown(env, reg);
+		if (reg->ref_obj_id == ref_obj_id) {
+			if (!env->allow_ptr_leaks)
+				__mark_reg_not_init(env, reg);
+			else
+				__mark_reg_unknown(env, reg);
+		}
 	}));
 
 	return 0;
-- 
2.25.1