tls: fix handling of zero-length records on the rx_list

kuba-moo · gregkh · commit 2902c3ebcca5 · 2025-08-28T16:26:16.000+02:00
commit 62708b9 upstream. Each recvmsg() call must process either - only contiguous DATA records (any number of them) - one non-DATA record If the next record has different type than what has already been processed we break out of the main processing loop. If the record has already been decrypted (which may be the case for TLS 1.3 where we don't know type until decryption) we queue the pending record to the rx_list. Next recvmsg() will pick it up from there. Queuing the skb to rx_list after zero-copy decrypt is not possible, since in that case we decrypted directly to the user space buffer, and we don't have an skb to queue (darg.skb points to the ciphertext skb for access to metadata like length). Only data records are allowed zero-copy, and we break the processing loop after each non-data record. So we should never zero-copy and then find out that the record type has changed. The corner case we missed is when the initial record comes from rx_list, and it's zero length. Reported-by: Muhammad Alifa Ramdhan <ramdhan@starlabs.sg> Reported-by: Billy Jheng Bing-Jhong <billy@starlabs.sg> Fixes: 84c61fe ("tls: rx: do not use the standard strparser") Reviewed-by: Sabrina Dubroca <sd@queasysnail.net> Link: https://patch.msgid.link/20250820021952.143068-1-kuba@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
@@ -1864,6 +1864,9 @@ int decrypt_skb(struct sock *sk, struct scatterlist *sgout)
 	return tls_decrypt_sg(sk, NULL, sgout, &darg);
 }
 
+/* All records returned from a recvmsg() call must have the same type.
+ * 0 is not a valid content type. Use it as "no type reported, yet".
+ */
 static int tls_record_content_type(struct msghdr *msg, struct tls_msg *tlm,
 				   u8 *control)
 {
@@ -2107,8 +2110,10 @@ int tls_sw_recvmsg(struct sock *sk,
 	if (err < 0)
 		goto end;
 
+	/* process_rx_list() will set @control if it processed any records */
 	copied = err;
-	if (len <= copied || (copied && control != TLS_RECORD_TYPE_DATA) || rx_more)
+	if (len <= copied || rx_more ||
+	    (control && control != TLS_RECORD_TYPE_DATA))
 		goto end;
 
 	target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
