tls: trim encrypted message to match the plaintext on short splice

[ Upstream commit ce5af41e3234425a40974696682163edfd21128c ]

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@google.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/66a0ae99c9efc15f88e9e56c1f58f902f442ce86.1760432043.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index f46550b96061ea1c2b63c5b73a2b8d998b6f0ccd..aac685daf66c4c9c47472f5fe644135df9f91ef2 100644 (file)
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1112,8 +1112,11 @@ alloc_encrypted:
                                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;