Ar Mer, 2006-08-23 am 13:35 -0700, ysgrifennodd Kylene Jo Hall:
> Example: The current process is running at the USER level and writing to
> a USER file in /home/user/. The process then attempts to read an
> UNTRUSTED file. The current process will become UNTRUSTED and the read
> allowed to proceed but first write access to all USER files is revoked
> including the ones it has open.
Which really doesn't mean anything in many cases because there are many
ways to get data out of a file handle once you had it opened for write
including sharing via non file handle paths.
You also have to deal with existing mmap() mappings and outstanding I/O.
So here are some ways to break it
SysV shared memory
mmap
or just race it:
Open the USER file
create a new thread
thread #1 create a pipe to a new process ("receiver")
thread #1 fill pipe
thread #1 issue write of buffer that will hold secret data
[blocks after check for rights]
thread #2
wait for thread #1 to block
read secret data into buffer
send signal to "receiver"
receiver now empties the pipe, the write completes and I get the
goodies.
This is why you need a proper implementation of revoke(2) in Linux. You
can't really do it any more easily.
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