[PATCH bpf-next] bpf: Fix error path under memory pressure

[Alexei Starovoitov <ast@xxxxxxxxxx>]

Restore the 'if (env->cur_state)' check that was incorrectly removed during
code move. Under memory pressure env->cur_state can be freed and zeroed inside
do_check(). Hence the check is necessary.

Fixes: 51c39bb1d5d1 ("bpf: Introduce function-by-function verification")
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
 kernel/bpf/verifier.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ca17dccc17ba..6defbec9eb62 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9594,8 +9594,13 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 
 	ret = do_check(env);
 out:
-	free_verifier_state(env->cur_state, true);
-	env->cur_state = NULL;
+	/* check for NULL is necessary, since cur_state can be freed inside
+	 * do_check() under memory pressure.
+	 */
+	if (env->cur_state) {
+		free_verifier_state(env->cur_state, true);
+		env->cur_state = NULL;
+	}
 	while (!pop_stack(env, NULL, NULL));
 	free_states(env);
 	if (ret)
-- 
2.23.0