bpf: Don't leak memory in bpf getsockopt when optlen == 0

optlen == 0 indicates that the kernel should ignore BPF buffer
and use the original one from the user. We, however, forget
to free the temporary buffer that we've allocated for BPF.

Fixes: d8fe449a9c51 ("bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE")
Reported-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210112162829.775079-1-sdf@google.com

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 6ec088a..96555a8 100644 (file)
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1391,12 +1391,13 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
                if (ctx.optlen != 0) {
                        *optlen = ctx.optlen;
                        *kernel_optval = ctx.optval;
+                       /* export and don't free sockopt buf */
+                       return 0;
                }
        }
 
 out:
-       if (ret)
-               sockopt_free_buf(&ctx);
+       sockopt_free_buf(&ctx);
        return ret;
 }