io_uring: fix task_work add use-after-free with SQPOLL

Overview

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

io_uring: fix task_work add use-after-free with SQPOLL

For SQPOLL, the sqpoll thread runs task_work off its own list and doesn't need to be told about it, so it can pop and complete a request as soon as mpscq_push() has published it. If that was the last request holding the ring alive, io_ring_exit_work() then frees the ctx, stops the thread, and with it the tctx, while io_req_normal_work_add() is still looking at both after the push:

BUG: KASAN: slab-use-after-free in io_req_normal_work_add+0x439/0x510 Read of size 4 at addr ff11000000ca0000 by task repro/55 (...) BUG: KASAN: slab-use-after-free in queue_work_on+0x25/0x70 Write of size 8 at addr ff11000000c3bd00 by task repro/55

Hold an RCU read lock across the add, like io_req_local_work_add() already does, and have io_ring_exit_work() wait for a grace period for SQPOLL rings as well before freeing the ctx.

Affected

• Linux >= af5d68f8892f8ee8f137648b79ceb2abc153a19b < 42b3332efacfd2140be4cd0dedad4fb96b8ae90e
• Linux >= af5d68f8892f8ee8f137648b79ceb2abc153a19b < 891bd8335a0de3bb15c3b797ce3026bbb0dbef6c
• Linux >= af5d68f8892f8ee8f137648b79ceb2abc153a19b < 395b25968fe854d4efaa19a8e9b7a5b6d1b3eea3
• Linux >= af5d68f8892f8ee8f137648b79ceb2abc153a19b < a92193c91e8839fe5fc209616ea95465ae4b919d
• Linux 6.9

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.