bpf: Fix error path under memory pressure

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

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ca17dccc17babfbc0bf6d11e27defa310576b2d1..6defbec9eb62bb123d150d1a1edaea56b6d298cd 100644 (file)
--- 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)