[PATCH] vt: fix unicode console freeing with a common interface

[PATCH] vt: fix unicode console freeing with a common interface

[Nicolas Pitre]

By directly using kfree() in different places we risk missing one if
it is switched to using vfree(), especially if the corresponding
vmalloc() is hidden away within a common abstraction.

Oh wait, that's exactly what happened here.

So let's fix this by creating a common abstraction for the free case
as well.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Reported-by: syzbot+0bfda3ade1ee9288a1be@syzkaller.appspotmail.com
Fixes: 9a98e7a80f95 ("vt: don't use kmalloc() for the unicode screen buffer")
Cc: <stable@vger.kernel.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index e5ffed795e..48a8199f78 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -365,9 +365,14 @@ static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)
 	return uniscr;
 }
 
+static void vc_uniscr_free(struct uni_screen *uniscr)
+{
+	vfree(uniscr);
+}
+
 static void vc_uniscr_set(struct vc_data *vc, struct uni_screen *new_uniscr)
 {
-	vfree(vc->vc_uni_screen);
+	vc_uniscr_free(vc->vc_uni_screen);
 	vc->vc_uni_screen = new_uniscr;
 }
 
@@ -1230,7 +1235,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
 	err = resize_screen(vc, new_cols, new_rows, user);
 	if (err) {
 		kfree(newscreen);
-		kfree(new_uniscr);
+		vc_uniscr_free(new_uniscr);
 		return err;
 	}
 

Re: [PATCH] vt: fix unicode console freeing with a common interface

[Sam Ravnborg]

Hi Nicolas

On Sat, May 02, 2020 at 11:01:07AM -0400, Nicolas Pitre wrote:
> By directly using kfree() in different places we risk missing one if
> it is switched to using vfree(), especially if the corresponding
> vmalloc() is hidden away within a common abstraction.
> 
> Oh wait, that's exactly what happened here.
> 
> So let's fix this by creating a common abstraction for the free case
> as well.
> 
> Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
> Reported-by: syzbot+0bfda3ade1ee9288a1be@syzkaller.appspotmail.com
> Fixes: 9a98e7a80f95 ("vt: don't use kmalloc() for the unicode screen buffer")
> Cc: <stable@vger.kernel.org>

Looks good.
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

Not the I know the code, but verified that no more kfree() was
used for vc_uni_screen.

	Sam

> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index e5ffed795e..48a8199f78 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -365,9 +365,14 @@ static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)
>  	return uniscr;
>  }
>  
> +static void vc_uniscr_free(struct uni_screen *uniscr)
> +{
> +	vfree(uniscr);
> +}
> +
>  static void vc_uniscr_set(struct vc_data *vc, struct uni_screen *new_uniscr)
>  {
> -	vfree(vc->vc_uni_screen);
> +	vc_uniscr_free(vc->vc_uni_screen);
>  	vc->vc_uni_screen = new_uniscr;
>  }
>  
> @@ -1230,7 +1235,7 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
>  	err = resize_screen(vc, new_cols, new_rows, user);
>  	if (err) {
>  		kfree(newscreen);
> -		kfree(new_uniscr);
> +		vc_uniscr_free(new_uniscr);
>  		return err;
>  	}
>