Re: [RFC 2/5] bus/pci: fix TOCTOU issue

[Thomas Monjalon <thomas@monjalon.net>]

+Cc Ferruh

06/11/2018 22:48, Stephen Hemminger:
> Using access followed by open causes a static analysis warning
> about Time of check versus Time of use. Also, access() and
> open() have different UID permission checks.
> 
> This is not a serious problem; but easy to fix by using errno instead.
> 
> Coverity issue: 300870
> Fixes: 4a928ef9f611 ("bus/pci: enable write combining during mapping")
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  drivers/bus/pci/linux/pci_uio.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/bus/pci/linux/pci_uio.c b/drivers/bus/pci/linux/pci_uio.c
> index 112ac51dddcc..8521fe63b0ae 100644
> --- a/drivers/bus/pci/linux/pci_uio.c
> +++ b/drivers/bus/pci/linux/pci_uio.c
> @@ -306,12 +306,11 @@ pci_uio_map_resource_by_index(struct rte_pci_device *dev, int res_idx,
>  			loc->domain, loc->bus, loc->devid,
>  			loc->function, res_idx);
>  
> -		if (access(devname, R_OK|W_OK) != -1) {
> -			fd = open(devname, O_RDWR);
> -			if (fd < 0)
> -				RTE_LOG(INFO, EAL, "%s cannot be mapped. "
> -					"Fall-back to non prefetchable mode.\n",
> -					devname);
> +		fd = open(devname, O_RDWR);
> +		if (fd < 0 && errno != ENOENT) {
> +			RTE_LOG(INFO, EAL, "%s cannot be mapped. "
> +				"Fall-back to non prefetchable mode.\n",
> +				devname);
>  		}
>  	}