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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Felix Maurer <fmaurer@redhat.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>
Subject: [PATCH 5.16 057/164] bpf: Do not try bpf_msg_push_data with len 0
Date:   Mon, 28 Feb 2022 18:23:39 +0100
Message-Id: <20220228172405.333864395@linuxfoundation.org>
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From: Felix Maurer <fmaurer@redhat.com>

commit 4a11678f683814df82fca9018d964771e02d7e6d upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/filter.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2711,6 +2711,9 @@ 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 {