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From: "tcs_kernel(腾讯云内核开发者)" <tcs_kernel@tencent.com>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"daniel.vetter@ffwll.ch" <daniel.vetter@ffwll.ch>,
	"yepeilin.cs@gmail.com" <yepeilin.cs@gmail.com>,
	"penguin-kernel@I-love.SAKURA.ne.jp" 
	<penguin-kernel@i-love.sakura.ne.jp>,
	"tzimmermann@suse.de" <tzimmermann@suse.de>,
	"george.kennedy@oracle.com" <george.kennedy@oracle.com>,
	"ducheng2@gmail.com" <ducheng2@gmail.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [Internet]Re: [PATCH] fbcon: Out-Of-Bounds write in sys_imageblit, add range check
Date: Tue, 27 Jul 2021 01:53:13 +0000	[thread overview]
Message-ID: <28F2D8E8-B519-40F6-B6CD-98A0FAD67CD7@tencent.com> (raw)
In-Reply-To: <YP68cQ4WVVusCv0N@ravnborg.org>

yres and vyres can be controlled by user mode paramaters, and cause p->vrows to become a negative value. While this value be passed to real_y function, the ypos will be out of screen range.
This is an out-of-bounds write bug.
I think updatescrollmode is the right place to validate values supplied by a user ioctl, because only here makes --operation,and 0 is a legal value before that.

Signed-off-by: Tencent Cloud System tcs_kernel@tencent.com

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 22bb3892f6bd..0970de46782f 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1956,11 +1956,12 @@ static void updatescrollmode(struct fbcon_display *p,
        int yres = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
        int vyres = FBCON_SWAP(ops->rotate, info->var.yres_virtual,
                                   info->var.xres_virtual);
+       int rows = vc->vc_rows;
 
        p->vrows = vyres/fh;
-       if (yres > (fh * (vc->vc_rows + 1)))
-               p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
-       if ((yres % fh) && (vyres % fh < yres % fh))
+       if ((yres > (fh * (rows + 1))) && (vyres >= (yres - (fh * rows))) && p->vrows)
+               p->vrows -= (yres - (fh * rows)) / fh;
+       if ((yres % fh) && (vyres % fh < yres % fh) && p->vrows)
                p->vrows--;
 }

在 2021/7/26 21:45,“Sam Ravnborg”<sam@ravnborg.org> 写入:

    Hi,
    On Mon, Jul 26, 2021 at 11:32:37AM +0000, tcs_kernel(腾讯云内核开发者) wrote:
    > yres and vyres can be controlled by user mode paramaters, and cause p->vrows to become a negative value. While this value be passed to real_y function, the ypos will be out of screen range.
    > This is an out-of-bounds write bug.

    Please investigate if you can validate the user-supplied values for yres
    and vyres earlier so the code never reaches the below statements.
    This would also make it much more explicit what is going on.

    	Sam

    > 
    > 
    > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
    > index 22bb3892f6bd..0970de46782f 100644
    > --- a/drivers/video/fbdev/core/fbcon.c
    > +++ b/drivers/video/fbdev/core/fbcon.c
    > @@ -1956,11 +1956,12 @@ static void updatescrollmode(struct fbcon_display *p,
    >         int yres = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
    >         int vyres = FBCON_SWAP(ops->rotate, info->var.yres_virtual,
    >                                    info->var.xres_virtual);
    > +       int rows = vc->vc_rows;
    >  
    >         p->vrows = vyres/fh;
    > -       if (yres > (fh * (vc->vc_rows + 1)))
    > -               p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
    > -       if ((yres % fh) && (vyres % fh < yres % fh))
    > +       if ((yres > (fh * (rows + 1))) && (vyres >= (yres - (fh * rows))) && p->vrows)
    > +               p->vrows -= (yres - (fh * rows)) / fh;
    > +       if ((yres % fh) && (vyres % fh < yres % fh) && p->vrows)
    >                 p->vrows--;
    >  }
    > 



  parent reply	other threads:[~2021-07-27  2:01 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 11:32 tcs_kernel(腾讯云内核开发者)
2021-07-26 13:00 ` gregkh
     [not found] ` <YP68cQ4WVVusCv0N@ravnborg.org>
2021-07-27  1:53   ` tcs_kernel(腾讯云内核开发者) [this message]
2021-07-27  5:35     ` [Internet]Re: " gregkh

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