patch "vt: don't use kmalloc() for the unicode screen buffer" added to tty-linus

This is a note to let you know that I've just added the patch titled

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

to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 9a98e7a80f95378c9ee0c644705e3b5aa54745f1 Mon Sep 17 00:00:00 2001
From: Nicolas Pitre <[email protected]>
Date: Sat, 28 Mar 2020 22:25:11 -0400
Subject: 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.

---
 drivers/tty/vt/vt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index 309a39197be0..3272759b1f3c 100644
@@ -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;
 }
 

2.26.2