n_tty: Fix calculation of size in canon_copy_from_read_buf

There was a hardcoded value of 4096 which should have been N_TTY_BUF_SIZE.
This caused reads from tty to fail with EFAULT when they shouldn't have
done if N_TTY_BUF_SIZE was declared to be something other than 4096.

Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index cc57a3a6b02b..759604e57b24 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2070,8 +2070,8 @@ static int canon_copy_from_read_buf(struct tty_struct *tty,
 
         size = N_TTY_BUF_SIZE - tail;
         n = eol - tail;
-        if (n > 4096)
-                n += 4096;
+        if (n > N_TTY_BUF_SIZE)
+                n += N_TTY_BUF_SIZE;
         n += found;
         c = n;