[PATCH 5.4 10/33] bpf: Dont leak memory in bpf getsockopt when optlen == 0

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Stanislav Fomichev <sdf@google.com>

commit 4be34f3d0731b38a1b24566b37fbb39500aaf3a2 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/bpf/cgroup.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1057,12 +1057,13 @@ int __cgroup_bpf_run_filter_setsockopt(s
 		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;
 }
 EXPORT_SYMBOL(__cgroup_bpf_run_filter_setsockopt);