linux-kernel - Re: [PATCH] of: overlay: Fix uninitialized vars in dup_and_fixup_symbol

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Date:   Tue, 19 Sep 2017 11:27:35 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>,
        Grant Likely <grant.likely@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: overlay: Fix uninitialized vars in
 dup_and_fixup_symbol_prop()

On 09/10/17 03:26, Geert Uytterhoeven wrote:
> With gcc 4.1.2:
> 
>     drivers/of/overlay.c: In function ‘dup_and_fixup_symbol_prop’:
>     drivers/of/overlay.c:108: warning: ‘overlay_name_len’ may be used uninitialized in this function
>     drivers/of/overlay.c:100: warning: ‘ovinfo’ may be used uninitialized in this function
> 
> Indeed, if ov->count == 0, both variables are uninitialized, which may
> lead to a crash when dereferencing ovinfo later.
> 
> Currently this is a false positive, as the sole creator of of_overlay
> structures (of_build_overlay_info(), introduced in commit
> 7518b5890d8ac366 ("of/overlay: Introduce DT overlay support") checks for
> this.
> 
> To prevent future issues, add a check for a zero ov->count to
> dup_and_fixup_symbol_prop().  Note that this does not get rid of the
> actual compiler warning.
> 
> Fixes: d1651b03c2df75db ("of: overlay: add overlay symbols to live device tree")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>  drivers/of/overlay.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 8ecfee31ab6d3874..ebe19e0f8e4d1f4b 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -108,7 +108,7 @@ static struct property *dup_and_fixup_symbol_prop(struct of_overlay *ov,
>  	int overlay_name_len;
>  	int target_path_len;
>  
> -	if (!prop->value)
> +	if (!ov->count || !prop->value)
>  		return NULL;
>  	symbol_path = prop->value;
>  
> 

I did not see this patch due to an overzealous spam filter.  I noticed it
when Rob replied with his applied email.

This check is not needed to prevent accessing overlay_name_len and ovinfo
when ov->count == 0.  That is already prevented by:

        if (k >= ov->count)
                goto err_free;

because k will be zero and ov->count will be zero.

-Frank