Linux CVE-2026-93191

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.cpipelined_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.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 ...

1. 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)