linux-kernel - RE: [PATCH] PCI: endpoint: use ffz() instead of find_first_zero

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Tue, 21 Nov 2017 13:01:48 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Niklas Cassel' <niklas.cassel@...s.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     Niklas Cassel <niklass@...s.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] PCI: endpoint: use ffz() instead of find_first_zero_bit()

From: Niklas Cassel
> Sent: 17 November 2017 09:43
> find_first_zero_bit()'s parameter 'size' is defined in bits,
> not in bytes.
> 
> Calling find_first_zero_bit() with the wrong size unit
> will lead to insidious bugs.
> 
> Fix this by using replacing find_first_zero_bit() with ffz(),
> since ffz() only works on a single 'unsigned long' and therefore
> does not need a size argument.
> 
> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>
> ---
>  drivers/pci/endpoint/pci-ep-cfs.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/pci-ep-cfs.c b/drivers/pci/endpoint/pci-ep-cfs.c
> index 4f74386c1ced..96b984685640 100644
> --- a/drivers/pci/endpoint/pci-ep-cfs.c
> +++ b/drivers/pci/endpoint/pci-ep-cfs.c
> @@ -108,8 +108,7 @@ static int pci_epc_epf_link(struct config_item *epc_item,
>  	if (ret)
>  		goto err_add_epf;
> 
> -	func_no = find_first_zero_bit(&epc_group->function_num_map,
> -				      sizeof(epc_group->function_num_map));
> +	func_no = ffz(epc_group->function_num_map);
>  	set_bit(func_no, &epc_group->function_num_map);
>  	epf->func_no = func_no;

Is set_bit() now setting the correct bit?
I'd guess that:
	epc_group->function_num_map |= 1ul << func_no;
would be more accurate?

	David