Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sat, 28 Mar 2020 22:25:11 -0400 (EDT)
From:   Nicolas Pitre <nico@fluxnic.net>
To:     gregkh@linuxfoundation.org
cc:     Chen Wandun <chenwandun@huawei.com>,
        Adam Borowski <kilobyte@angband.pl>, jslaby@suse.com,
        daniel.vetter@ffwll.ch, sam@ravnborg.org, b.zolnierkie@samsung.com,
        lukas@wunner.de, ghalat@redhat.com, linux-kernel@vger.kernel.org
Subject: [PATCH v2] vt: don't use kmalloc() for the unicode screen buffer
In-Reply-To: <nycvar.YSQ.7.76.2003281745280.2671@knanqh.ubzr>
Message-ID: <nycvar.YSQ.7.76.2003282214210.2671@knanqh.ubzr>
References: <nycvar.YSQ.7.76.2003281745280.2671@knanqh.ubzr>
User-Agent: Alpine 2.21 (LFD 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@fluxnic.net>
Cc: <stable@vger.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;
 }