netdev - [PATCH net v2 1/2] net: tls, fix WARNIING in __sk_msg

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Date: Fri, 12 Jan 2024 16:32:57 -0800
From: John Fastabend <john.fastabend@...il.com>
To: netdev@...r.kernel.org,
	eadavis@...com,
	kuba@...nel.org
Cc: john.fastabend@...il.com,
	bpf@...r.kernel.org,
	borisp@...dia.com
Subject: [PATCH net v2 1/2] net: tls, fix WARNIING in __sk_msg_free

A splice with MSG_SPLICE_PAGES will cause tls code to use the
tls_sw_sendmsg_splice path in the TLS sendmsg code to move the user
provided pages from the msg into the msg_pl. This will loop over the
msg until msg_pl is full, checked by sk_msg_full(msg_pl). The user
can also set the MORE flag to hint stack to delay sending until receiving
more pages and ideally a full buffer.

If the user adds more pages to the msg than can fit in the msg_pl
scatterlist (MAX_MSG_FRAGS) we should ignore the MORE flag and send
the buffer anyways.

What actually happens though is we abort the msg to msg_pl scatterlist
setup and then because we forget to set 'full record' indicating we
can no longer consume data without a send we fallthrough to the 'continue'
path which will check if msg_data_left(msg) has more bytes to send and
then attempts to fit them in the already full msg_pl. Then next
iteration of sender doing send will encounter a full msg_pl and throw
the warning in the syzbot report.

To fix simply check if we have a full_record in splice code path and
if not send the msg regardless of MORE flag.

Reported-and-tested-by: syzbot+f2977222e0e95cec15c8@...kaller.appspotmail.com
Reported-by: Edward Adam Davis <eadavis@...com>
Fixes: fe1e81d4f73b ("tls/sw: Support MSG_SPLICE_PAGES")
Reviewed-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 net/tls/tls_sw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index e37b4d2e2acd..31e8a94dfc11 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1052,7 +1052,11 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 			if (ret < 0)
 				goto send_end;
 			tls_ctx->pending_open_record_frags = true;
-			if (full_record || eor || sk_msg_full(msg_pl))
+
+			if (sk_msg_full(msg_pl))
+				full_record = true;
+
+			if (full_record || eor)
 				goto copied;
 			continue;
 		}
-- 
2.33.0