Re: [Qemu-devel] [PATCH] pci-assign: avoid pointless stat

[Eric Blake]

On 01/04/2017 09:05 AM, Paolo Bonzini wrote:
> Just check the errno value after fopen and follow it with fstat.
> This shuts up Coverity's complaint about TOC/TOU violation.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  hw/i386/pci-assign-load-rom.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

> 
> diff --git a/hw/i386/pci-assign-load-rom.c b/hw/i386/pci-assign-load-rom.c
> index 0d8e4b2..fd59076 100644
> --- a/hw/i386/pci-assign-load-rom.c
> +++ b/hw/i386/pci-assign-load-rom.c
> @@ -39,19 +39,19 @@ void *pci_assign_dev_load_option_rom(PCIDevice *dev, 
> struct Object *owner,
>               "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/rom",
>               domain, bus, slot, function);
>  
> -    if (stat(rom_file, &st)) {
> -        if (errno != ENOENT) {
> -            error_report("pci-assign: Invalid ROM.");
> -        }
> -        return NULL;
> -    }
> -
>      /* Write "1" to the ROM file to enable it */
>      fp = fopen(rom_file, "r+");
>      if (fp == NULL) {
> -        error_report("pci-assign: Cannot open %s: %s", rom_file, 
> strerror(errno));
> +        if (errno != ENOENT) {
> +            error_report("pci-assign: Cannot open %s: %s", rom_file, 
> strerror(errno));
> +        }
>          return NULL;
>      }
> +    if (fstat(fileno(fp), &st) == -1) {
> +        error_report("pci-assign: Cannot stat %s: %s", rom_file, 
> strerror(errno));
> +        goto close_rom;

fstat() failure after fopen() success is quite unlikely, but I suppose
it is still possible in some weird situations.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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