[Qemu-devel] [PATCH] pci-assign: do not test path with access() before opening

[Qemu-devel] [PATCH] pci-assign: do not test path with access() before opening

[Paolo Bonzini]

Using access() is a time-of-check/time-of-use race condition.  It is
okay to use them to provide better error messages, but that is pretty
much it.

In this case we can get the same error from fopen(), so just use
strerror and errno there---which actually improves the error
message most of the time.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/i386/pci-assign-load-rom.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/hw/i386/pci-assign-load-rom.c b/hw/i386/pci-assign-load-rom.c
index 34a3a7e..e40b586 100644
--- a/hw/i386/pci-assign-load-rom.c
+++ b/hw/i386/pci-assign-load-rom.c
@@ -45,14 +45,10 @@ void *pci_assign_dev_load_option_rom(PCIDevice *dev, struct Object *owner,
         return NULL;
     }
 
-    if (access(rom_file, F_OK)) {
-        error_report("pci-assign: Insufficient privileges for %s", rom_file);
-        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));
         return NULL;
     }
     val = 1;
-- 
2.5.0

Re: [Qemu-devel] [PATCH] pci-assign: do not test path with access() before opening

[Eric Blake]

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On 11/02/2015 07:17 AM, Paolo Bonzini wrote:
> Using access() is a time-of-check/time-of-use race condition.  It is
> okay to use them to provide better error messages, but that is pretty
> much it.
> 
> In this case we can get the same error from fopen(), so just use
> strerror and errno there---which actually improves the error
> message most of the time.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/i386/pci-assign-load-rom.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

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


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Re: [Qemu-devel] [PATCH] pci-assign: do not test path with access() before opening

[Michael Tokarev]

02.11.2015 17:17, Paolo Bonzini wrote:
> Using access() is a time-of-check/time-of-use race condition.  It is
> okay to use them to provide better error messages, but that is pretty
> much it.
> 
> In this case we can get the same error from fopen(), so just use
> strerror and errno there---which actually improves the error
> message most of the time.

Applied to -trivial, thank you!

/mjt