In the Linux kernel, the following vulnerability has been resolved: smack: fix incorrect task context in smack_msg_queue_msgrcv The smack_

In the Linux kernel, the following vulnerability has been resolved:

smack: fix incorrect task context in smack_msg_queue_msgrcv

The smack_msg_queue_msgrcv() function incorrectly checks
the permissions of the 'current' task instead of the
'target' task.

In the msgsnd() syscall path, if a receiver is already waiting,
the pipelined_send() optimization is used to push the message
directly to the receiver task:

 1ipc/msg.c`pipelined_send():
 2` smp_store_release(&msr->r_msg, msg)

In this case, the 'sender' (current) task performs the check
on behalf of the 'receiver' task (msr->r_tsk, passed as the
'target' parameter):

ipc/msg.cpipelined_send(): security_msg_queue_msgrcv(,, target := msr->r_tsk,,)

However, smack_msg_queue_msgrcv() ignores the 'target' and
checks 'current':

smack_msg_queue_msgrcv(…)
` smk_curacc_msq(isp, MAY_READWRITE); // current task

'current' MAY satisfy smack_msg_queue_msgrcv r/w requirement,
but 'target' (the receiver task) might NOT;
as a result, an unauthorized receiver gets the message,
violating MAC policy.

Test:

1. create a sysv message queue with label “foo”
2. echo "bar foo r" >/smack/load2
3. msgrcv(,,,0,MSG_NOERROR) in "bar"-labeled task.
   The task is waiting for the messages ...
4. msgsnd() from a "foo"-labeled task:
   "bar"-labeled task gets the message.

This patch fixes the issue by checking permission on the
'target' task instead of 'current'.

(2008-02-04, Casey Schaufler)