linux-kernel - Re: [PATCH 4.4 28/31] video: hgafb: fix potential NULL pointer dereference

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Message-ID: <20210525204704.GA12631@duo.ucw.cz>
Date:   Tue, 25 May 2021 22:47:04 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Ferenc Bakonyi <fero@...ma.obuda.kando.hu>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Igor Matheus Andrade Torrente <igormtorrente@...il.com>
Subject: Re: [PATCH 4.4 28/31] video: hgafb: fix potential NULL pointer
 dereference

Hi!

> From: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
> 
> commit dc13cac4862cc68ec74348a80b6942532b7735fa upstream.
> 
> The return of ioremap if not checked, and can lead to a NULL to be
> assigned to hga_vram. Potentially leading to a NULL pointer
> dereference.
> 
> The fix adds code to deal with this case in the error label and
> changes how the hgafb_probe handles the return of hga_card_detect.

This will break hgafb completely, right? And crash system without hga
card as a bonus.

> +++ b/drivers/video/fbdev/hgafb.c
> @@ -285,6 +285,8 @@ static int hga_card_detect(void)
>  	hga_vram_len  = 0x08000;
>  
>  	hga_vram = ioremap(0xb0000, hga_vram_len);
> +	if (!hga_vram)
> +		return -ENOMEM;
>  
>  	if (request_region(0x3b0, 12, "hgafb"))
>  		release_io_ports = 1;
> @@ -344,13 +346,18 @@ static int hga_card_detect(void)
>  			hga_type_name = "Hercules";
>  			break;
>  	}
> -	return 1;
> +	return 0;

Ok, so calling convention is now "0 means detected".


> @@ -548,13 +555,11 @@ static struct fb_ops hgafb_ops = {
>  static int hgafb_probe(struct platform_device *pdev)
>  {
>  	struct fb_info *info;
> +	int ret;
...
> +	ret = hga_card_detect();
> +	if (!ret)
> +		return ret;
>  
>  	printk(KERN_INFO "hgafb: %s with %ldK of memory detected.\n",
>  		hga_type_name, hga_vram_len/1024);
> 

If the card is detected, 0 is returned, !0 is true, and we abort
detection....

								Pavel
								
Signed-off-by: Pavel Machek <pavel@...x.de>

diff --git a/drivers/video/fbdev/hgafb.c b/drivers/video/fbdev/hgafb.c
index c35f217db53f..d6a95ea49c64 100644
--- a/drivers/video/fbdev/hgafb.c
+++ b/drivers/video/fbdev/hgafb.c
@@ -282,7 +282,7 @@ static int hga_card_detect(void)
 	void __iomem *p, *q;
 	unsigned short p_save, q_save;
 
-	hga_vram_len  = 0x08000;
+	hga_vram_len = 0x08000;
 
 	hga_vram = ioremap(0xb0000, hga_vram_len);
 	if (!hga_vram)
@@ -558,7 +558,7 @@ static int hgafb_probe(struct platform_device *pdev)
 	int ret;
 
 	ret = hga_card_detect();
-	if (!ret)
+	if (ret)
 		return ret;
 
 	printk(KERN_INFO "hgafb: %s with %ldK of memory detected.\n",


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