netdev - [PATCH net 1/7] tls: trim encrypted message to match the plaintext on short splice

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Message-ID: <66a0ae99c9efc15f88e9e56c1f58f902f442ce86.1760432043.git.sd@queasysnail.net>
Date: Tue, 14 Oct 2025 11:16:56 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: netdev@...r.kernel.org
Cc: Sabrina Dubroca <sd@...asysnail.net>,
	kuba@...nel.org,
	jannh@...gle.com,
	john.fastabend@...il.com
Subject: [PATCH net 1/7] tls: trim encrypted message to match the plaintext on short splice

During tls_sw_sendmsg_locked, we pre-allocate the encrypted message
for the size we're expecting to send during the current iteration, but
we may end up sending less, for example when splicing: if we're
getting the data from small fragments of memory, we may fill up all
the slots in the skmsg with less data than expected.

In this case, we need to trim the encrypted message to only the length
we actually need, to avoid pushing uninitialized bytes down the
underlying TCP socket.

Fixes: fe1e81d4f73b ("tls/sw: Support MSG_SPLICE_PAGES")
Reported-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
---
 net/tls/tls_sw.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index daac9fd4be7e..36ca3011ab87 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1112,8 +1112,11 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 				goto send_end;
 			tls_ctx->pending_open_record_frags = true;
 
-			if (sk_msg_full(msg_pl))
+			if (sk_msg_full(msg_pl)) {
 				full_record = true;
+				sk_msg_trim(sk, msg_en,
+					    msg_pl->sg.size + prot->overhead_size);
+			}
 
 			if (full_record || eor)
 				goto copied;
-- 
2.51.0