vt: don't hardcode the mem allocation upper bound

BugLink: https://bugs.launchpad.net/bugs/1877461
commit 2717769e204e83e65b8819c5e2ef3e5b6639b270 upstream.

The code in vc_do_resize() bounds the memory allocation size to avoid
exceeding MAX_ORDER down the kzalloc() call chain and generating a
runtime warning triggerable from user space. However, not only is it
unwise to use a literal value here, but MAX_ORDER may also be
configurable based on CONFIG_FORCE_MAX_ZONEORDER.
Let's use KMALLOC_MAX_SIZE instead.

Note that prior commit bb1107f7c605 ("mm, slab: make sure that
KMALLOC_MAX_SIZE will fit into MAX_ORDER") the KMALLOC_MAX_SIZE value
could not be relied upon.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Cc: <stable@vger.kernel.org> # v4.10+
Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.2003281702410.2671@knanqh.ubzr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 56fb417c934cb13dfbf496248441423401b9d824..fc227a09c40efbd4b99b6c77a6e06ab16f2a28de 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -901,7 +901,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
        if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
                return 0;
 
-       if (new_screen_size > (4 << 20))
+       if (new_screen_size > KMALLOC_MAX_SIZE)
                return -EINVAL;
        newscreen = kzalloc(new_screen_size, GFP_USER);
        if (!newscreen)