6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Penglei Jiang superman.xpt@gmail.com
[ Upstream commit ac0b8b327a5677dc6fecdf353d808161525b1ff0 ]
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.
Reported-by: syzbot+531502bbbe51d2f769f4@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/682b06a5.a70a0220.3849cf.00b3.GAE@google.com Fixes: 3fcb9d17206e ("io_uring/sqpoll: statistics of the true utilization of sq threads") Signed-off-by: Penglei Jiang superman.xpt@gmail.com Link: https://lore.kernel.org/r/20250610171801.70960-1-superman.xpt@gmail.com [axboe: massage commit message] Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/fdinfo.c | 12 ++++++++++-- io_uring/sqpoll.c | 9 ++++----- 2 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c index ecdbe473a49f7..c6c624eb9866d 100644 --- a/io_uring/fdinfo.c +++ b/io_uring/fdinfo.c @@ -146,18 +146,26 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
if (has_lock && (ctx->flags & IORING_SETUP_SQPOLL)) { struct io_sq_data *sq = ctx->sq_data; + struct task_struct *tsk;
+ rcu_read_lock(); + tsk = rcu_dereference(sq->thread); /* * sq->thread might be NULL if we raced with the sqpoll * thread termination. */ - if (sq->thread) { + if (tsk) { + get_task_struct(tsk); + rcu_read_unlock(); + getrusage(tsk, RUSAGE_SELF, &sq_usage); + put_task_struct(tsk); sq_pid = sq->task_pid; sq_cpu = sq->sq_cpu; - getrusage(sq->thread, RUSAGE_SELF, &sq_usage); sq_total_time = (sq_usage.ru_stime.tv_sec * 1000000 + sq_usage.ru_stime.tv_usec); sq_work_time = sq->work_time; + } else { + rcu_read_unlock(); } }
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c index 430922c541681..b0f17a1220ecd 100644 --- a/io_uring/sqpoll.c +++ b/io_uring/sqpoll.c @@ -277,7 +277,8 @@ static int io_sq_thread(void *data) /* offload context creation failed, just exit */ if (!current->io_uring) { mutex_lock(&sqd->lock); - sqd->thread = NULL; + rcu_assign_pointer(sqd->thread, NULL); + put_task_struct(current); mutex_unlock(&sqd->lock); goto err_out; } @@ -386,7 +387,8 @@ static int io_sq_thread(void *data) io_sq_tw(&retry_list, UINT_MAX);
io_uring_cancel_generic(true, sqd); - sqd->thread = NULL; + rcu_assign_pointer(sqd->thread, NULL); + put_task_struct(current); list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) atomic_or(IORING_SQ_NEED_WAKEUP, &ctx->rings->sq_flags); io_run_task_work(); @@ -507,9 +509,6 @@ __cold int io_sq_offload_create(struct io_ring_ctx *ctx, ret = -EINVAL; goto err; } - - if (task_to_put) - put_task_struct(task_to_put); return 0; err_sqpoll: complete(&ctx->sq_data->exited);