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From: Peilin Ye <yepeilin.cs@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: linux-fbdev@vger.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org,
	David Laight <David.Laight@aculab.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers
Date: Thu, 24 Sep 2020 12:59:19 -0400	[thread overview]
Message-ID: <20200924165919.GA880812@PWN> (raw)
In-Reply-To: <20200924154516.GL4282@kadam>

On Thu, Sep 24, 2020 at 06:45:16PM +0300, Dan Carpenter wrote:
> Smatch has a tool to show where struct members are set.
> 
> `~/smatch/smatch_data/db/smdb.py where console_font height`
> 
> It's not perfect and this output comes from allmodconfig on yesterday's
> linux-next.
> 
> regards,
> dan carpenter

Wow, thank you for the really interesting information!

> drivers/video/console/vgacon.c | vgacon_init                    | (struct console_font)->height | 0-32
> drivers/video/console/vgacon.c | vgacon_adjust_height           | (struct console_font)->height | 1-32
> drivers/video/fbdev/core/fbcon.c | fbcon_startup                  | (struct console_font)->height | 6,8,10-11,14,16,18,22,32
> drivers/video/fbdev/core/fbcon.c | fbcon_init                     | (struct console_font)->height | 6,8,10-11,14,16,18,22,32
> drivers/video/fbdev/core/fbcon.c | fbcon_do_set_font              | (struct console_font)->height | 0-u32max
> drivers/video/fbdev/core/fbcon.c | fbcon_set_def_font             | (struct console_font)->height | 6,8,10-11,14,16,18,22,32
> drivers/usb/misc/sisusbvga/sisusb_con.c | sisusbcon_init                 | (struct console_font)->height | 0-u32max

In looking at this one,
	c->vc_font.height = sisusb->current_font_height;

`sisusb->current_font_height` is only set in sisusbcon_do_font_op():
		sisusb->current_font_height = fh;

and...

> drivers/usb/misc/sisusbvga/sisusb_con.c | sisusbcon_do_font_op           | (struct console_font)->height | 1-32

...sisusbcon_do_font_op() is called in four places, with an `fh` of either
16, `sisusb->font_backup_height`, or `font->height`. The latter two cases
all come from sisusbcon_font_set(), whose dispatcher, con_font_set()
gurantees that `font->height` is less than or equal to 32, as shown by
Smatch here.

> drivers/tty/vt/vt_ioctl.c      | vt_k_ioctl                     | (struct console_font)->height | ignore
> drivers/tty/vt/vt_ioctl.c      | vt_resizex                     | (struct console_font)->height | 0-u32max
> drivers/tty/vt/vt_ioctl.c      | vt_ioctl                       | (struct console_font)->height | ignore
> drivers/tty/vt/vt_ioctl.c      | vt_compat_ioctl                | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | vc_allocate                    | (struct console_font)->height | 0
> drivers/tty/vt/vt.c            | vt_resize                      | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | do_con_write                   | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | con_unthrottle                 | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | con_flush_chars                | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | con_shutdown                   | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | con_cleanup                    | (struct console_font)->height | ignore
> drivers/tty/vt/vt.c            | con_init                       | (struct console_font)->height | 0
> drivers/tty/vt/vt.c            | con_font_set                   | (struct console_font)->height | 1-32
> drivers/tty/vt/vt.c            | con_font_default               | (struct console_font)->height | 0-u32max
> drivers/tty/vt/selection.c     | paste_selection                | (struct console_font)->height | ignore

I will go through the list starting from these "0-u32max" cases. Thanks
again!

Peilin Ye

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  reply	other threads:[~2020-09-24 16:59 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <0000000000006b9e8d059952095e@google.com>
2020-09-24 13:38 ` [Linux-kernel-mentees] [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers Peilin Ye
2020-09-24 13:40   ` [Linux-kernel-mentees] [PATCH 1/3] fbdev, newport_con: Move FONT_EXTRA_WORDS macros into linux/font.h Peilin Ye
2020-09-24 13:42     ` [Linux-kernel-mentees] [PATCH 2/3] Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts Peilin Ye
2020-09-24 13:43       ` [Linux-kernel-mentees] [PATCH 3/3] fbcon: Fix global-out-of-bounds read in fbcon_get_font() Peilin Ye
2020-09-24 14:09   ` [Linux-kernel-mentees] [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers Greg Kroah-Hartman
2020-09-24 14:25     ` Peilin Ye
2020-09-24 14:42     ` David Laight
2020-09-24 15:30       ` Peilin Ye
2020-09-24 15:45         ` Dan Carpenter
2020-09-24 16:59           ` Peilin Ye [this message]
2020-09-25  8:38     ` Daniel Vetter
2020-09-25  6:46   ` Jiri Slaby
2020-09-25 10:13     ` Peilin Ye
2020-09-25 13:25       ` Daniel Vetter
2020-09-25 15:35         ` Peilin Ye
2020-09-29  9:09           ` Daniel Vetter
2020-09-29  9:44             ` Peilin Ye
2020-09-29 12:34         ` Peilin Ye
2020-09-29 14:38           ` Daniel Vetter
2020-09-30  7:11             ` Peilin Ye
2020-09-30  9:53               ` Daniel Vetter
2020-09-30 10:55                 ` Peilin Ye
2020-09-30 11:25                   ` Daniel Vetter
2020-09-30 11:52                     ` Greg Kroah-Hartman
2020-09-30 12:58                       ` Peilin Ye
2020-09-30  5:26           ` Jiri Slaby
2020-09-30  7:16             ` Peilin Ye

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