> On Tue, 22 May 2012, Du, ChangbinX wrote:
>
> > > diff --git a/tools/usb/testusb.c b/tools/usb/testusb.c index
> > > 6e0f567..82d7c59 100644
> > > --- a/tools/usb/testusb.c
> > > +++ b/tools/usb/testusb.c
> > > @@ -358,6 +358,7 @@ static const char *usbfs_dir_find(void) {
> > > static char usbfs_path_0[] = "/dev/usb/devices";
> > > static char usbfs_path_1[] = "/proc/bus/usb/devices";
> > > + static char udev_usb_path[] = "/dev/bus/usb";
> > >
> > > static char *const usbfs_paths[] = {
> > > usbfs_path_0, usbfs_path_1
> > > @@ -376,6 +377,10 @@ static const char *usbfs_dir_find(void)
> > > }
> > > } while (++it != end);
> > >
> > > + /* real device-nodes managed by udev */
> > > + if (access(udev_usb_path, F_OK) == 0)
> > > + return udev_usb_path;
> > > +
> > > return NULL;
> > > }
> > >
> >
> > Two issues with this: F_OK only guarantees that the path exists, it
> > does not guarantee that it is readable like this function guarantees
> > for usbfs_paths, and access() shouldn't be used because of its
> > security implications, you're better off using open() and testing for fd.
> >
> > Hello, David. I think this function doesn't need check the permission.
> > What this function need do is to find the usbfs mount point. If the
> > path exists but cannot read, we cannot report as it's not exits. And
> > when we read files, open() will return an error and user can check if
> > it's need to upgrade his access right.
> >
>
> Your email client doesn't seem to be quoting messages correctly :)
>
> Anyway, this patch is inconsistent with the rest of the function. The other two
> paths are checked with open(O_RDONLY) followed by a close() to address my
> second comment and we certainly wouldn't want to return a path that exists by
> is unreadable: we'd want to fallback to one of the other possibilities. So if
> anybody is going to extend this in the future like you have, it would be possible
> to return /dev/bus/usb even though we can't read it. That's a bad result.
>
> Please consider doing it the proper way: by doing open(O_RDONLY), close()
> instead of access() -- if you don't understand why, read access(2) -- and in an
> extendable way.
I see. Thanks for your comments. I will correct and resend it again.
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