CVE-2026-99254

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

io uring: don't flood a cancelling task with task work

io ring exit work() asks each task which has used the ring to remove its tctx node, by task work, and repeats that until the list is empty. io tctx exit cb() doesn't touch the node while the task is in io uring cancel generic(), which removes all the nodes at its end. So the work item queues the callback again as soon as it has completed, for nothing.

That is more than a waste of time. task work run() only returns when it finds the list empty. If the rings are released from inside the cancellation, because requests of other rings held the last references to their files, up to 64 work items keep sending callbacks to the one task which is running them. It never finds the list empty, never gets back to the cancellation, the nodes stay, and so it goes on: a task with 60 pairs of rings which poll each other ran 280000 callbacks in 5 seconds, 20 seconds after exit group(). It ends when all the senders happen to be late at the same time. Until then the task keeps a CPU and the work items busy.

An exiting task can't be killed meanwhile. execve() cancels the requests in the same way, so a live task can get stuck there as well, for minutes. If it takes more than five, the work items run into the WARN ON ONCE(time after(jiffies, timeout)) of io ring exit work(). No privilege is needed for any of this.

If the callback has met a task in cancellation, wait a little before it is sent again. Nobody has to wake the work item up for that: either the node is gone by then, or it is the turn of the next round.