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Date:   Mon, 2 Apr 2018 12:09:03 -0700
From:   Ram Pai <linuxram@us.ibm.com>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Bjorn Helgaas <bhelgaas@google.com>, linux-kernel@vger.kernel.org,
        Michael Henders <hendersm@shaw.ca>
Subject: Re: [PATCH] resource: Fix integer overflow at reallocation
Reply-To: Ram Pai <linuxram@us.ibm.com>
References: <20180402071616.27177-1-tiwai@suse.de>
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On Mon, Apr 02, 2018 at 09:16:16AM +0200, Takashi Iwai wrote:
> We've got a bug report indicating a kernel panic at booting on an
> x86-32 system, and it turned out to be the invalid resource assigned
> after reallocation.  __find_resource() first aligns the resource start
> address and resets the end address with start+size-1 accordingly, then
> checks whether it's contained.  Here the end address may overflow the
> integer, although resource_contains() still returns true because the
> function validates only start and end address.  So this ends up with
> returning an invalid resource (start > end).
> 
> There was already an attempt to cover such a problem in the commit
> 47ea91b4052d ("Resource: fix wrong resource window calculation"), but
> this case is an overseen one.
> 
> This patch adds the validity check of the newly calculated resource
> for avoiding the integer overflow problem.

Should we move this check "alloc.start <= alloc.end" into resource_contains()?
Doing so will catch all uses of such erroneous (overflowing) resources.

RP

> 
> Bugzilla: https://urldefense.proofpoint.com/v2/url?u=http-3A__bugzilla.opensuse.org_show-5Fbug.cgi-3Fid-3D1086739&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=m-UrKChQVkZtnPpjbF6YY99NbT8FBByQ-E-ygV8luxw&m=FoiwlR-LTJ9_EBQsLYSCqXuWrGhU1lXycdvhbaK7wOk&s=clxOtFUIAMlPNwQJZTaKnmIta9pMtJ8XprmwVd-ylvo&e=
> Fixes: 23c570a67448 ("resource: ability to resize an allocated resource")
> Reported-and-tested-by: Michael Henders <hendersm@shaw.ca>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
> 
> Bjorn, I send this to you since the bug hits during PCI init, although
> the culprit is in generic resource management.
> 
>  kernel/resource.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index e270b5048988..2af6c03858b9 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -651,7 +651,8 @@ static int __find_resource(struct resource *root, struct resource *old,
>  			alloc.start = constraint->alignf(constraint->alignf_data, &avail,
>  					size, constraint->align);
>  			alloc.end = alloc.start + size - 1;
> -			if (resource_contains(&avail, &alloc)) {
> +			if (alloc.start <= alloc.end &&
> +			    resource_contains(&avail, &alloc)) {
>  				new->start = alloc.start;
>  				new->end = alloc.end;
>  				return 0;
> -- 
> 2.16.2

-- 
Ram Pai