netdev - [bpf PATCH 8/9] bpf: sockmap/tls, tls_push_record can not handle zero length skmsg

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Date:   Wed, 08 Jan 2020 21:16:11 +0000
From:   John Fastabend <john.fastabend@...il.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, john.fastabend@...il.com, ast@...nel.org,
        daniel@...earbox.net
Subject: [bpf PATCH 8/9] bpf: sockmap/tls,
 tls_push_record can not handle zero length skmsg

When passed a zero length skmsg tls_push_record() causes a NULL ptr
deref. To resolve for fixes do a simple length check at start of
routine.

To create this case a user can create a BPF program to pop all the
data off the message then return SK_PASS. Its not a very practical
or useful thing to do so we mark it unlikely.

Fixes: d3b18ad31f93d ("tls: add bpf support to sk_msg handling")
Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 net/tls/tls_sw.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 21c7725d17ca..0326e916ab01 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -680,6 +680,9 @@ static int tls_push_record(struct sock *sk, int flags,
 	msg_pl = &rec->msg_plaintext;
 	msg_en = &rec->msg_encrypted;
 
+	if (unlikely(!msg_pl->sg.size))
+		return 0;
+
 	split_point = msg_pl->apply_bytes;
 	split = split_point && split_point < msg_pl->sg.size;
 	if (unlikely((!split &&