CVE-2025-21633

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

io_uring/sqpoll: zero sqd->thread on tctx errors

Syzkeller reports:

BUG: KASAN: slab-use-after-free in thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
Read of size 8 at addr ffff88803578c510 by task syz.2.3223/27552
 Call Trace:
  <TASK>
  ...
  kasan_report+0x143/0x180 mm/kasan/report.c:602
  thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
  thread_group_cputime_adjusted+0xa6/0x340 kernel/sched/cputime.c:639
  getrusage+0x1000/0x1340 kernel/sys.c:1863
  io_uring_show_fdinfo+0xdfe/0x1770 io_uring/fdinfo.c:197
  seq_show+0x608/0x770 fs/proc/fd.c:68
  ...

That's due to sqd->task not being cleared properly in cases where
SQPOLL task tctx setup fails, which can essentially only happen with
fault injection to insert allocation errors.