On Tue, Jun 3, 2008 at 1:22 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Jun 03, 2008 at 01:13:00PM +0200, Miklos Szeredi wrote: >> > > I'm not sure of the correct way to get the required nameidata (to do a >> > > vfs_permission() call) from the file descriptor. Can you give me a >> > > tip there? >> > >> > Could you point me at the right way of doing this? >> >> You don't need nameidata for this at all. Just call permission() with >> a NULL nameidata. >> >> Ugly API? Yes, will be cleaned up if we manage to find some common >> ground with the VFS maintainers. > > As soon as I'm done with sysctls... > > FWIW, I very much doubt that you are right wrt required permissions, though. > AFAICS, intent here is "if you can write to file, you can touch the timestamps > anyway" and having descriptor opened for write gives that, current permissions > be damned. The standard is pretty clear on this point: [[ Only a process with the effective user ID equal to the user ID of the file, or with write access to the file, or with appropriate privileges may use futimens( ) or utimensat( ) with a null pointer as the times argument or with both tv_nsec fields set to the special value UTIME_NOW. ]] The crucial words here are "a process ... with write access to the file" -- in other words, the permissions are determined by the process's credentials, not by the access mode of the file descriptor. I was not 100% sure on that to start with, so I did check it out with one of the folk at The Open Group, to make sure of my understanding. -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
