linux-kernel - [PATCH v2] vt: don't use kmalloc() for the unicode screen buffer

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Date:   Sat, 28 Mar 2020 22:25:11 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     gregkh@...uxfoundation.org
cc:     Chen Wandun <chenwandun@...wei.com>,
        Adam Borowski <kilobyte@...band.pl>, jslaby@...e.com,
        daniel.vetter@...ll.ch, sam@...nborg.org, b.zolnierkie@...sung.com,
        lukas@...ner.de, ghalat@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2] vt: don't use kmalloc() for the unicode screen buffer

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@...xnic.net>
Cc: <stable@...r.kernel.org>

---

Changes since v1:

- Added missing include, found by kbuild test robot.
  Strange that my own build doesn't complain.

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 15d2769805..d9eb5661e9 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -81,6 +81,7 @@
 #include <linux/errno.h>
 #include <linux/kd.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <linux/major.h>
 #include <linux/mm.h>
 #include <linux/console.h>
@@ -350,7 +351,7 @@ 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 +367,7 @@ 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;
 }