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Message-ID: <6efc0d2a-c2af-947c-d928-104e3add1650@gmx.de>
Date:   Wed, 24 Aug 2022 22:04:38 +0200
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Subject: Re: [PATCH] fbcon: Properly revert changes when vc_resize() failed
Content-Language: en-US
To:     Shigeru Yoshida <syoshida@redhat.com>
Cc:     linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org,
        syzbot+a168dbeaaa7778273c1b@syzkaller.appspotmail.com
References: <20220818181336.3504010-1-syoshida@redhat.com>
From:   Helge Deller <deller@gmx.de>
In-Reply-To: <20220818181336.3504010-1-syoshida@redhat.com>
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Hi Shigeru,

On 8/18/22 20:13, Shigeru Yoshida wrote:
> fbcon_do_set_font() calls vc_resize() when font size is changed.
> However, if if vc_resize() failed, current implementation doesn't
> revert changes for font size, and this causes inconsistent state.
>
> syzbot reported unable to handle page fault due to this issue [1].
> syzbot's repro uses fault injection which cause failure for memory
> allocation, so vc_resize() failed.
>
> This patch fixes this issue by properly revert changes for font
> related date when vc_resize() failed.
>
> Link: https://syzkaller.appspot.com/bug?id=3D3443d3a1fa6d964dd7310a0cb16=
96d165a3e07c4 [1]
> Reported-by: syzbot+a168dbeaaa7778273c1b@syzkaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>

applied.

Thank you!
Helge

> ---
>  drivers/video/fbdev/core/fbcon.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core=
/fbcon.c
> index cf9ac4da0a82..825b012debe7 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -2401,15 +2401,21 @@ static int fbcon_do_set_font(struct vc_data *vc,=
 int w, int h, int charcount,
>  	struct fb_info *info =3D fbcon_info_from_console(vc->vc_num);
>  	struct fbcon_ops *ops =3D info->fbcon_par;
>  	struct fbcon_display *p =3D &fb_display[vc->vc_num];
> -	int resize;
> +	int resize, ret, old_userfont, old_width, old_height, old_charcount;
>  	char *old_data =3D NULL;
>
>  	resize =3D (w !=3D vc->vc_font.width) || (h !=3D vc->vc_font.height);
>  	if (p->userfont)
>  		old_data =3D vc->vc_font.data;
>  	vc->vc_font.data =3D (void *)(p->fontdata =3D data);
> +	old_userfont =3D p->userfont;
>  	if ((p->userfont =3D userfont))
>  		REFCOUNT(data)++;
> +
> +	old_width =3D vc->vc_font.width;
> +	old_height =3D vc->vc_font.height;
> +	old_charcount =3D vc->vc_font.charcount;
> +
>  	vc->vc_font.width =3D w;
>  	vc->vc_font.height =3D h;
>  	vc->vc_font.charcount =3D charcount;
> @@ -2425,7 +2431,9 @@ static int fbcon_do_set_font(struct vc_data *vc, i=
nt w, int h, int charcount,
>  		rows =3D FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
>  		cols /=3D w;
>  		rows /=3D h;
> -		vc_resize(vc, cols, rows);
> +		ret =3D vc_resize(vc, cols, rows);
> +		if (ret)
> +			goto err_out;
>  	} else if (con_is_visible(vc)
>  		   && vc->vc_mode =3D=3D KD_TEXT) {
>  		fbcon_clear_margins(vc, 0);
> @@ -2435,6 +2443,21 @@ static int fbcon_do_set_font(struct vc_data *vc, =
int w, int h, int charcount,
>  	if (old_data && (--REFCOUNT(old_data) =3D=3D 0))
>  		kfree(old_data - FONT_EXTRA_WORDS * sizeof(int));
>  	return 0;
> +
> +err_out:
> +	p->fontdata =3D old_data;
> +	vc->vc_font.data =3D (void *)old_data;
> +
> +	if (userfont) {
> +		p->userfont =3D old_userfont;
> +		REFCOUNT(data)--;
> +	}
> +
> +	vc->vc_font.width =3D old_width;
> +	vc->vc_font.height =3D old_height;
> +	vc->vc_font.charcount =3D old_charcount;
> +
> +	return ret;
>  }
>
>  /*