io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo()

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

io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo()

syzbot reports:

BUG: KASAN: slab-use-after-free in getrusage+0x1109/0x1a60

Read of size 8 at addr ffff88810de2d2c8 by task a.out/304

CPU: 0 UID: 0 PID: 304 Comm: a.out Not tainted 6.16.0-rc1 #1 PREEMPT(voluntary)

Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

Call Trace:

<TASK>

dump_stack_lvl+0x53/0x70

print_report+0xd0/0x670

? __pfx__raw_spin_lock_irqsave+0x10/0x10

? getrusage+0x1109/0x1a60

kasan_report+0xce/0x100

? getrusage+0x1109/0x1a60

getrusage+0x1109/0x1a60

? __pfx_getrusage+0x10/0x10

__io_uring_show_fdinfo+0x9fe/0x1790

? ksys_read+0xf7/0x1c0

? do_syscall_64+0xa4/0x260

? vsnprintf+0x591/0x1100

? __pfx___io_uring_show_fdinfo+0x10/0x10

? __pfx_vsnprintf+0x10/0x10

? mutex_trylock+0xcf/0x130

? __pfx_mutex_trylock+0x10/0x10

? __pfx_show_fd_locks+0x10/0x10

? io_uring_show_fdinfo+0x57/0x80

io_uring_show_fdinfo+0x57/0x80

seq_show+0x38c/0x690

seq_read_iter+0x3f7/0x1180

? inode_set_ctime_current+0x160/0x4b0

seq_read+0x271/0x3e0

? __pfx_seq_read+0x10/0x10

? __pfx__raw_spin_lock+0x10/0x10

? __mark_inode_dirty+0x402/0x810

? selinux_file_permission+0x368/0x500

? file_update_time+0x10f/0x160

vfs_read+0x177/0xa40

? __pfx___handle_mm_fault+0x10/0x10

? __pfx_vfs_read+0x10/0x10

? mutex_lock+0x81/0xe0

? __pfx_mutex_lock+0x10/0x10

? fdget_pos+0x24d/0x4b0

ksys_read+0xf7/0x1c0

? __pfx_ksys_read+0x10/0x10

? do_user_addr_fault+0x43b/0x9c0

do_syscall_64+0xa4/0x260

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f0f74170fc9

Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 8

RSP: 002b:00007fffece049e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000000

RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0f74170fc9

RDX: 0000000000001000 RSI: 00007fffece049f0 RDI: 0000000000000004

RBP: 00007fffece05ad0 R08: 0000000000000000 R09: 00007fffece04d90

R10: 0000000000000000 R11: 0000000000000206 R12: 00005651720a1100

R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

</TASK>

Allocated by task 298:

kasan_save_stack+0x33/0x60

kasan_save_track+0x14/0x30

__kasan_slab_alloc+0x6e/0x70

kmem_cache_alloc_node_noprof+0xe8/0x330

copy_process+0x376/0x5e00

create_io_thread+0xab/0xf0

io_sq_offload_create+0x9ed/0xf20

io_uring_setup+0x12b0/0x1cc0

do_syscall_64+0xa4/0x260

entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22:

kasan_save_stack+0x33/0x60

kasan_save_track+0x14/0x30

kasan_save_free_info+0x3b/0x60

__kasan_slab_free+0x37/0x50

kmem_cache_free+0xc4/0x360

rcu_core+0x5ff/0x19f0

handle_softirqs+0x18c/0x530

run_ksoftirqd+0x20/0x30

smpboot_thread_fn+0x287/0x6c0

kthread+0x30d/0x630

ret_from_fork+0xef/0x1a0

ret_from_fork_asm+0x1a/0x30

Last potentially related work creation:

kasan_save_stack+0x33/0x60

kasan_record_aux_stack+0x8c/0xa0

__call_rcu_common.constprop.0+0x68/0x940

__schedule+0xff2/0x2930

__cond_resched+0x4c/0x80

mutex_lock+0x5c/0xe0

io_uring_del_tctx_node+0xe1/0x2b0

io_uring_clean_tctx+0xb7/0x160

io_uring_cancel_generic+0x34e/0x760

do_exit+0x240/0x2350

do_group_exit+0xab/0x220

__x64_sys_exit_group+0x39/0x40

x64_sys_call+0x1243/0x1840

do_syscall_64+0xa4/0x260

entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810de2cb00

which belongs to the cache task_struct of size 3712

The buggy address is located 1992 bytes inside of

freed 3712-byte region [ffff88810de2cb00, ffff88810de2d980)

which is caused by the task_struct pointed to by sq->thread being

released while it is being used in the function

__io_uring_show_fdinfo(). Holding ctx->uring_lock does not prevent ehre

relase or exit of sq->thread.

Fix this by assigning and looking up ->thread under RCU, and grabbing a

reference to the task_struct. This e

---truncated---