This is a note to let you know that I've just added the patch titled
fbcon: prevent user font height or width change from causing
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 39b3cffb8cf3111738ea993e2757ab382253d86a Mon Sep 17 00:00:00 2001
From: George Kennedy <george.kennedy@xxxxxxxxxx>
Date: Fri, 31 Jul 2020 12:33:11 -0400
Subject: fbcon: prevent user font height or width change from causing
potential out-of-bounds access
Add a check to fbcon_resize() to ensure that a possible change to user font
height or user font width will not allow a font data out-of-bounds access.
NOTE: must use original charcount in calculation as font charcount can
change and cannot be used to determine the font data allocated size.
Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Reported-by: syzbot+38a3699c7eaf165b97a6@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/1596213192-6635-1-git-send-email-george.kennedy@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/video/fbdev/core/fbcon.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 8a31fc2b2258..66167830fefd 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2191,6 +2191,9 @@ static void updatescrollmode(struct fbcon_display *p,
}
}
+#define PITCH(w) (((w) + 7) >> 3)
+#define CALC_FONTSZ(h, p, c) ((h) * (p) * (c)) /* size = height * pitch * charcount */
+
static int fbcon_resize(struct vc_data *vc, unsigned int width,
unsigned int height, unsigned int user)
{
@@ -2200,6 +2203,24 @@ static int fbcon_resize(struct vc_data *vc, unsigned int width,
struct fb_var_screeninfo var = info->var;
int x_diff, y_diff, virt_w, virt_h, virt_fw, virt_fh;
+ if (ops->p && ops->p->userfont && FNTSIZE(vc->vc_font.data)) {
+ int size;
+ int pitch = PITCH(vc->vc_font.width);
+
+ /*
+ * If user font, ensure that a possible change to user font
+ * height or width will not allow a font data out-of-bounds access.
+ * NOTE: must use original charcount in calculation as font
+ * charcount can change and cannot be used to determine the
+ * font data allocated size.
+ */
+ if (pitch <= 0)
+ return -EINVAL;
+ size = CALC_FONTSZ(vc->vc_font.height, pitch, FNTCHARCNT(vc->vc_font.data));
+ if (size > FNTSIZE(vc->vc_font.data))
+ return -EINVAL;
+ }
+
virt_w = FBCON_SWAP(ops->rotate, width, height);
virt_h = FBCON_SWAP(ops->rotate, height, width);
virt_fw = FBCON_SWAP(ops->rotate, vc->vc_font.width,
@@ -2652,7 +2673,7 @@ static int fbcon_set_font(struct vc_data *vc, struct console_font *font,
int size;
int i, csum;
u8 *new_data, *data = font->data;
- int pitch = (font->width+7) >> 3;
+ int pitch = PITCH(font->width);
/* Is there a reason why fbconsole couldn't handle any charcount >256?
* If not this check should be changed to charcount < 256 */
@@ -2668,7 +2689,7 @@ static int fbcon_set_font(struct vc_data *vc, struct console_font *font,
if (fbcon_invalid_charcount(info, charcount))
return -EINVAL;
- size = h * pitch * charcount;
+ size = CALC_FONTSZ(h, pitch, charcount);
new_data = kmalloc(FONT_EXTRA_WORDS * sizeof(int) + size, GFP_USER);
--
2.28.0
