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Subject[OOPS?] FD & Device Locking...
Date
I found out the following two problems:
- Only 4096 fd's opened at one time..

I tried to ncftp 3.0 the kernel-source 2.2.9 (all the seperate files)
from my dual to my single.
But as ncftp opens as any sockets, the system runs out...
and then it takes upto the TIME_WAIT until the sockets are fread..
And as the sockets are all in use (probably it are the fd's).
Thus a standard kernel without tweaking can't handle more than 4096
requests.. which is a possible vulnerability.
In the time that the fd's are all used it isn't possible to telnet
out... or make any other connections.
Both the client and the server had problems with it.

- Whenever one opens a device, you can still open it again and read/write
from/to it...

Though you can't mount it twice, cause it's checked for by the mount
function, it is possible to open it even if it is mounted... This can
cause unpredictable results whenever you've a mount and then write to
it... But that can only be done by authorized users who know what they
are doing... The major problem is that it ain't possible to lock out a
device from remount/open etc. As my changer device (see url at bottom)
opens a device, one still can mount that device !after! one has mounted
the /dev/changer device (which has opened the device already)....
What to do about that?
PS: I thought of a read-many / write-only-one lock in kdev_open() but...
but then the bootprocess has to be changed too...

PS2: Linus/Alan, the /dev/changer is stable enough for the 2.3.x tree...
so go put it in...

Greets,
Jeroen Massar

--
jmassar@unfix.org -- http://unfix.org -- http://unfix.org/projects/changer


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