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fbcon: prevent user font height or width change from causing potential out-of-bounds access

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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@oracle.com>
Cc: stable <stable@vger.kernel.org>
Reported-by: syzbot+38a3699c7eaf165b97a6@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/1596213192-6635-1-git-send-email-george.kennedy@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
George Kennedy 2020-07-31 12:33:11 -04:00 committed by Greg Kroah-Hartman
parent f8d1653dae
commit 39b3cffb8c
1 changed files with 23 additions and 2 deletions
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25
drivers/video/fbdev/core/fbcon.c
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@ -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);