Commit d97aa066 authored by Jiri Slaby (SUSE)'s avatar Jiri Slaby (SUSE) Committed by Greg Kroah-Hartman
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tty: n_tty: use uint for space returned by tty_write_room() 



tty_write_room() returns an "unsigned int". So in case some insane
driver (like my tty test driver) returns (legitimate) UINT_MAX from its
tty_operations::write_room(), n_tty is confused on several places.

For example, in process_output_block(), the result of tty_write_room()
is stored into (signed) "int". So this UINT_MAX suddenly becomes -1. And
that is extended to ssize_t and returned from process_output_block().
This causes a write() to such a node to receive -EPERM (which is -1).

Fix that by using proper "unsigned int" and proper "== 0" test. And
return 0 constant directly in that "if", so that it is immediately clear
what is returned ("space" equals to 0 at that point).

Similarly for process_output() and __process_echoes().

Note this does not fix any in-tree driver as of now.

If you want "Fixes: something", it would be commit 03b3b1a2 ("tty:
make tty_operations::write_room return uint"). I intentionally do not
mark this patch by a real tag below.

Signed-off-by: default avatarJiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250317070046.24386-6-jirislaby@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d2e38e71

drivers/tty/n_tty.c

+7 −6
Original line number Diff line number Diff line
@@ -488,7 +488,8 @@ static int do_output_char(u8 c, struct tty_struct *tty, int space) 
static int process_output(u8 c, struct tty_struct *tty)

{

	struct n_tty_data *ldata = tty->disc_data;

	int	space, retval;

	unsigned int space;

	int retval;



	mutex_lock(&ldata->output_lock);
@@ -524,16 +525,16 @@ static ssize_t process_output_block(struct tty_struct *tty, 
				    const u8 *buf, unsigned int nr)

{

	struct n_tty_data *ldata = tty->disc_data;

	int	space;

	unsigned int space;

	int i;

	const u8 *cp;



	mutex_lock(&ldata->output_lock);



	space = tty_write_room(tty);

	if (space <= 0) {

	if (space == 0) {

		mutex_unlock(&ldata->output_lock);

		return space;

		return 0;

	}

	if (nr > space)

		nr = space;
@@ -698,7 +699,7 @@ static int n_tty_process_echo_ops(struct tty_struct *tty, size_t *tail, 
static size_t __process_echoes(struct tty_struct *tty)

{

	struct n_tty_data *ldata = tty->disc_data;

	int	space, old_space;

	unsigned int space, old_space;

	size_t tail;

	u8 c;