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FAILED: patch "[PATCH] tty: n_gsm: fix invalid gsmtty_write_room() result" failed to apply to 5.15-stable tree

PATCH [email protected] 1 participant 1 message May 16, 2022

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The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9361ebfbb79fd1bc8594a487c01ad52cdaa391ea Mon Sep 17 00:00:00 2001
From: Daniel Starke <[email protected]>
Date: Wed, 4 May 2022 10:17:33 +0200
Subject: [PATCH] tty: n_gsm: fix invalid gsmtty_write_room() result

gsmtty_write() does not prevent the user to use the full fifo size of 4096 bytes as allocated in gsm_dlci_alloc(). However, gsmtty_write_room() tries to limit the return value by 'TX_SIZE' and returns a negative value if the fifo has more than 'TX_SIZE' bytes stored. This is obviously wrong as 'TX_SIZE' is defined as 512.
Define 'TX_SIZE' to the fifo size and use it accordingly for allocation to keep the current behavior. Return the correct remaining size of the fifo in gsmtty_write_room() via kfifo_avail().

Fixes e1eaea46bb40 ("tty: n_gsm line discipline")
Cc [email protected]
Signed-off-by Daniel Starke <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Greg Kroah-Hartman <[email protected]>
drivers/tty/n_gsm.c +3 -4
index bcb714031d69..fd8b86dde525 100644
@@ -137,6 +137,7 @@ struct gsm_dlci {
 	int retries;
 	/* Uplink tty if active */
 	struct tty_port port;	/* The tty bound to this DLCI if there is one */
+#define TX_SIZE		4096    /* Must be power of 2. */
 	struct kfifo fifo;	/* Queue fifo for the DLCI */
 	int adaption;		/* Adaption layer in use */
 	int prev_adaption;

@@ -1731,7 +1732,7 @@ static struct gsm_dlci *gsm_dlci_alloc(struct gsm_mux *gsm, int addr)
 		return NULL;
 	spin_lock_init(&dlci->lock);
 	mutex_init(&dlci->mutex);
-	if (kfifo_alloc(&dlci->fifo, 4096, GFP_KERNEL) < 0) {
+	if (kfifo_alloc(&dlci->fifo, TX_SIZE, GFP_KERNEL) < 0) {
 		kfree(dlci);
 		return NULL;
 	}

@@ -2976,8 +2977,6 @@ static struct tty_ldisc_ops tty_ldisc_packet = {
  *	Virtual tty side
  */
 
-#define TX_SIZE		512
-
 /**
  *	gsm_modem_upd_via_data	-	send modem bits via convergence layer
  *	@dlci: channel

@@ -3217,7 +3216,7 @@ static unsigned int gsmtty_write_room(struct tty_struct *tty)
 	struct gsm_dlci *dlci = tty->driver_data;
 	if (dlci->state == DLCI_CLOSED)
 		return 0;
-	return TX_SIZE - kfifo_len(&dlci->fifo);
+	return kfifo_avail(&dlci->fifo);
 }
 
 static unsigned int gsmtty_chars_in_buffer(struct tty_struct *tty)