Messages in this thread | | | Date | Sat, 05 Dec 2009 09:42:33 -0500 | From | Andy Lutomirski <> | Subject | Re: [PATCH v3] vfs: new O_NODE open flag |
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Miklos Szeredi wrote: > On Wed, 2 Dec 2009, Alan Cox wrote: >>> You're still missing the point. O_NODE is like a hard link, except >>> the reference doesn't come from the filesystem but from a file >>> descriptor. From udev's perspective there's no difference. >> I don't think I am missing the point here. You have a reference to an >> object in the fs but you don't have a reference to the driver underneath >> s the driver can change on you *while* you have the O_NODE open and fd >> live. That cannot happen with a hard link and open. >> >> It isn't the same thing as far as I can see. You don't have the barrier >> between the operations that occurs in the real open/close case because >> they lock the driver. > > The file descriptor opened with O_NODE allows exaclactly the same > operations that a hard link to the device would, nothing more. It's > just a link to the *node*, except it doesn't increment the link count, > the driver is irrelevant. >
I don't know what that means. Do you mean that if:
root creates /dev/foo with 0666 perms eviluser opens /dev/foo with O_NODE root chmods /dev/foo to 0000 root unlinks /dev/foo
then eviluser can't open /proc/self/fd/whatever for O_RDRW
Because if eviluser could still open /proc/self/fd/whatever for O_RDRW (or anything else for that matter if O_NODE isn't set) then you have a security problem.
--Andy
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