[lkml]   [2009]   [Dec]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v3] vfs: new O_NODE open flag
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.


 \ /
  Last update: 2009-12-05 15:53    [W:0.062 / U:3.516 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site