[PATCH] vt: don't use kmalloc() for the unicode screen buffer

From: Nicolas Pitre
Date: Sat Mar 28 2020 - 17:59:31 EST


Even if the actual screen size is bounded in vc_do_resize(), the unicode
buffer is still a little more than twice the size of the glyph buffer
and may exceed MAX_ORDER down the kmalloc() path. This can be triggered
from user space.

Since there is no point having a physically contiguous buffer here,
let's avoid the above issue as well as reducing pressure on high order
allocations by using vmalloc() instead.

Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 15d2769805..7c10edb648 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -350,7 +350,7 @@ static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)
/* allocate everything in one go */
memsize = cols * rows * sizeof(char32_t);
memsize += rows * sizeof(char32_t *);
- p = kmalloc(memsize, GFP_KERNEL);
+ p = vmalloc(memsize);
if (!p)
return NULL;

@@ -366,7 +366,7 @@ static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)

static void vc_uniscr_set(struct vc_data *vc, struct uni_screen *new_uniscr)
{
- kfree(vc->vc_uni_screen);
+ vfree(vc->vc_uni_screen);
vc->vc_uni_screen = new_uniscr;
}