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@oracle.com 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@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@or... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);