From: Felix Maurer <fmaurer@redhat.com>
Date: Wed, 9 Feb 2022 16:55:26 +0100
Subject: bpf: Do not try bpf_msg_push_data with len 0
Patch-mainline: v5.17-rc6
Git-commit: 4a11678f683814df82fca9018d964771e02d7e6d
References: jsc#PED-1368

If bpf_msg_push_data() is called with len 0 (as it happens during
selftests/bpf/test_sockmap), we do not need to do anything and can
return early.

Calling bpf_msg_push_data() with len 0 previously lead to a wrong ENOMEM
error: we later called get_order(copy + len); if len was 0, copy + len
was also often 0 and get_order() returned some undefined value (at the
moment 52). alloc_pages() caught that and failed, but then bpf_msg_push_data()
returned ENOMEM. This was wrong because we are most probably not out of
memory and actually do not need any additional memory.

Fixes: 6fff607e2f14b ("bpf: sk_msg program helper bpf_msg_push_data")
Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/df69012695c7094ccb1943ca02b4920db3537466.1644421921.git.fmaurer@redhat.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 net/core/filter.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2727,6 +2727,9 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_
 	if (unlikely(flags))
 		return -EINVAL;
 
+	if (unlikely(len == 0))
+		return 0;
+
 	/* First find the starting scatterlist element */
 	i = msg->sg.start;
 	do {