bpf: liveness: Handle ERR_PTR from get_outer_instance() in propagate_to_outer_instance()

propagate_to_outer_instance() calls get_outer_instance() and then uses the
returned pointer to reset/commit stack write marks. When get_outer_instance()
fails (e.g., __lookup_instance() returns -ENOMEM), it may return an ERR_PTR.
Without a check, the code dereferences this error pointer.

Protect the call with IS_ERR() and propagate the error.

Reported-by: kernel-patches-review-bot (kernel-patches/bpf#10006 (comment))
Signed-off-by: Shardul Bankar <[email protected]>
v2: Drop Fixes tag per Eduard’s review (not a functional bug).

Author: shardulsb08

kernel/bpf/liveness.c

@@ -524,6 +524,8 @@ static int propagate_to_outer_instance(struct bpf_verifier_env *env,
 
 	this_subprog_start = callchain_subprog_start(callchain);
 	outer_instance = get_outer_instance(env, instance);
+	if (IS_ERR(outer_instance))
+		return PTR_ERR(outer_instance);
 	callsite = callchain->callsites[callchain->curframe - 1];
 
 	reset_stack_write_marks(env, outer_instance, callsite);