linux-cve-announce - CVE-2025-38106: io_uring: fix use-after-free of sq->thread in __io_uring_show

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Message-ID: <2025070322-CVE-2025-38106-8de3@gregkh>
Date: Thu,  3 Jul 2025 10:35:23 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38106: io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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 ensures that it cannot get released
while fdinfo is using it.

[axboe: massage commit message]

The Linux kernel CVE team has assigned CVE-2025-38106 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.9 with commit 3fcb9d17206e31630f802a3ab52081d1342b8ed9 and fixed in 6.12.34 with commit af8c13f9ee040b9a287ba246cf0055f7c77b7cc8
	Issue introduced in 6.9 with commit 3fcb9d17206e31630f802a3ab52081d1342b8ed9 and fixed in 6.15.3 with commit d0932758a0a77b38ba1b39564f3b7aba12407061
	Issue introduced in 6.9 with commit 3fcb9d17206e31630f802a3ab52081d1342b8ed9 and fixed in 6.16-rc2 with commit ac0b8b327a5677dc6fecdf353d808161525b1ff0

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38106
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	io_uring/fdinfo.c
	io_uring/sqpoll.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/af8c13f9ee040b9a287ba246cf0055f7c77b7cc8
	https://git.kernel.org/stable/c/d0932758a0a77b38ba1b39564f3b7aba12407061
	https://git.kernel.org/stable/c/ac0b8b327a5677dc6fecdf353d808161525b1ff0