bpf, ktls: Fix data corruption when using bpf_msg_pop_data() in ktls

JIRA: https://issues.redhat.com/browse/RHEL-115640

commit 178f6a5
Author: Jiayuan Chen <jiayuan.chen@linux.dev>
Date:   Mon Jun 9 10:08:52 2025 +0800

    bpf, ktls: Fix data corruption when using bpf_msg_pop_data() in ktls

    When sending plaintext data, we initially calculated the corresponding
    ciphertext length. However, if we later reduced the plaintext data length
    via socket policy, we failed to recalculate the ciphertext length.

    This results in transmitting buffers containing uninitialized data during
    ciphertext transmission.

    This causes uninitialized bytes to be appended after a complete
    "Application Data" packet, leading to errors on the receiving end when
    parsing TLS record.

    Fixes: d3b18ad ("tls: add bpf support to sk_msg handling")
    Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Reviewed-by: John Fastabend <john.fastabend@gmail.com>
    Acked-by: Jakub Kicinski <kuba@kernel.org>
    Link: https://lore.kernel.org/bpf/20250609020910.397930-2-jiayuan.chen@linux.dev

Signed-off-by: Sabrina Dubroca <sdubroca@redhat.com>

Author: Sabrina Dubroca

net/tls/tls_sw.c

@@ -865,6 +865,19 @@ static int bpf_exec_tx_verdict(struct sk_msg *msg, struct sock *sk,
 		delta = msg->sg.size;
 		psock->eval = sk_psock_msg_verdict(sk, psock, msg);
 		delta -= msg->sg.size;
+
+		if ((s32)delta > 0) {
+			/* It indicates that we executed bpf_msg_pop_data(),
+			 * causing the plaintext data size to decrease.
+			 * Therefore the encrypted data size also needs to
+			 * correspondingly decrease. We only need to subtract
+			 * delta to calculate the new ciphertext length since
+			 * ktls does not support block encryption.
+			 */
+			struct sk_msg *enc = &ctx->open_rec->msg_encrypted;
+
+			sk_msg_trim(sk, enc, enc->sg.size - delta);
+		}
 	}
 	if (msg->cork_bytes && msg->cork_bytes > msg->sg.size &&
 	    !enospc && !full_record) {