From: Alexei Starovoitov <ast@kernel.org>
Date: Tue, 21 Jan 2020 18:41:38 -0800
Subject: bpf: Fix error path under memory pressure
Patch-mainline: v5.6-rc1
Git-commit: f59bbfc2f6099e8655f9e8f585e10ffde17176d0
References: bsc#1177028

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")
Reported-by: syzbot+b296579ba5015704d9fa@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200122024138.3385590-1-ast@kernel.org
Acked-by: Gary Lin <glin@suse.com>
---
 kernel/bpf/verifier.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9606,8 +9606,13 @@ static int do_check_common(struct bpf_ve
 
 	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)