Affected: Linux

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:

ipc/msg.c`pipelined_send(): ` 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.c`pipelined_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)