KASAN: use-after-free Read in io_async_task_func

KASAN: use-after-free Read in io_async_task_func

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    fc80c51f Merge tag 'kbuild-v5.9' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17601ab2900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d48472fcc2f68903
dashboard link: https://syzkaller.appspot.com/bug?extid=9b260fc33297966f5a8e
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=174272b2900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9b260fc33297966f5a8e@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:56 [inline]
BUG: KASAN: use-after-free in atomic64_read include/asm-generic/atomic-instrumented.h:837 [inline]
BUG: KASAN: use-after-free in atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
BUG: KASAN: use-after-free in __mutex_unlock_slowpath+0x88/0x590 kernel/locking/mutex.c:1237
Read of size 8 at addr ffff8880952503c0 by task syz-executor.1/23201

CPU: 0 PID: 23201 Comm: syz-executor.1 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1f0/0x31e lib/dump_stack.c:118
 print_address_description+0x66/0x620 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report+0x132/0x1d0 mm/kasan/report.c:530
 check_memory_region_inline mm/kasan/generic.c:183 [inline]
 check_memory_region+0x2b5/0x2f0 mm/kasan/generic.c:192
 instrument_atomic_read include/linux/instrumented.h:56 [inline]
 atomic64_read include/asm-generic/atomic-instrumented.h:837 [inline]
 atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
 __mutex_unlock_slowpath+0x88/0x590 kernel/locking/mutex.c:1237
 io_async_task_func+0x485/0x610 fs/io_uring.c:4689
 task_work_run+0x137/0x1c0 kernel/task_work.c:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:139 [inline]
 exit_to_user_mode_prepare+0xfa/0x1c0 kernel/entry/common.c:166
 syscall_exit_to_user_mode+0x5e/0x1a0 kernel/entry/common.c:241
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45ce69
Code: 2d b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 fb b5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f6719775c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: fffffffffffffffe RBX: 0000000000004f40 RCX: 000000000045ce69
RDX: 0000000000000043 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 000000000118c010 R08: 0000000020000140 R09: 0000000000000000
R10: 0000000020000000 R11: 0000000000000246 R12: 000000000118bfcc
R13: 00007fff62cc118f R14: 00007f67197769c0 R15: 000000000118bfcc

Allocated by task 23153:
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc+0x100/0x130 mm/kasan/common.c:461
 kmem_cache_alloc_trace+0x1f6/0x2f0 mm/slab.c:3550
 kmalloc include/linux/slab.h:554 [inline]
 kzalloc include/linux/slab.h:666 [inline]
 io_ring_ctx_alloc fs/io_uring.c:1030 [inline]
 io_uring_create fs/io_uring.c:8308 [inline]
 io_uring_setup fs/io_uring.c:8401 [inline]
 __do_sys_io_uring_setup fs/io_uring.c:8407 [inline]
 __se_sys_io_uring_setup+0x5ce/0x2c70 fs/io_uring.c:8404
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 5:
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track+0x3d/0x70 mm/kasan/common.c:56
 kasan_set_free_info+0x17/0x30 mm/kasan/generic.c:355
 __kasan_slab_free+0xdd/0x110 mm/kasan/common.c:422
 __cache_free mm/slab.c:3418 [inline]
 kfree+0x10a/0x220 mm/slab.c:3756
 process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
 worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
 kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Last call_rcu():
 kasan_save_stack+0x27/0x50 mm/kasan/common.c:48
 kasan_record_aux_stack+0x7b/0xb0 mm/kasan/generic.c:346
 __call_rcu kernel/rcu/tree.c:2894 [inline]
 call_rcu+0x139/0x840 kernel/rcu/tree.c:2968
 __percpu_ref_switch_to_atomic lib/percpu-refcount.c:192 [inline]
 __percpu_ref_switch_mode+0x2c1/0x4f0 lib/percpu-refcount.c:237
 percpu_ref_kill_and_confirm+0x8f/0x130 lib/percpu-refcount.c:350
 percpu_ref_kill include/linux/percpu-refcount.h:136 [inline]
 io_ring_ctx_wait_and_kill+0x3c/0x570 fs/io_uring.c:7797
 io_uring_release+0x59/0x70 fs/io_uring.c:7829
 __fput+0x34f/0x7b0 fs/file_table.c:281
 task_work_run+0x137/0x1c0 kernel/task_work.c:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:139 [inline]
 exit_to_user_mode_prepare+0xfa/0x1c0 kernel/entry/common.c:166
 syscall_exit_to_user_mode+0x5e/0x1a0 kernel/entry/common.c:241
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Second to last call_rcu():
 kasan_save_stack+0x27/0x50 mm/kasan/common.c:48
 kasan_record_aux_stack+0x7b/0xb0 mm/kasan/generic.c:346
 __call_rcu kernel/rcu/tree.c:2894 [inline]
 call_rcu+0x139/0x840 kernel/rcu/tree.c:2968
 __percpu_ref_switch_to_atomic lib/percpu-refcount.c:192 [inline]
 __percpu_ref_switch_mode+0x2c1/0x4f0 lib/percpu-refcount.c:237
 percpu_ref_kill_and_confirm+0x8f/0x130 lib/percpu-refcount.c:350
 percpu_ref_kill include/linux/percpu-refcount.h:136 [inline]
 io_ring_ctx_wait_and_kill+0x3c/0x570 fs/io_uring.c:7797
 io_uring_release+0x59/0x70 fs/io_uring.c:7829
 __fput+0x34f/0x7b0 fs/file_table.c:281
 task_work_run+0x137/0x1c0 kernel/task_work.c:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:139 [inline]
 exit_to_user_mode_prepare+0xfa/0x1c0 kernel/entry/common.c:166
 syscall_exit_to_user_mode+0x5e/0x1a0 kernel/entry/common.c:241
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff888095250000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 960 bytes inside of
 2048-byte region [ffff888095250000, ffff888095250800)
The buggy address belongs to the page:
page:000000005a2c89d9 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x95250
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00024ca6c8 ffffea00024d8c48 ffff8880aa440800
raw: 0000000000000000 ffff888095250000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888095250280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888095250300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888095250380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff888095250400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888095250480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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Re: KASAN: use-after-free Read in io_async_task_func

[Jens Axboe]

On 8/11/20 12:47 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    fc80c51f Merge tag 'kbuild-v5.9' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17601ab2900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d48472fcc2f68903
> dashboard link: https://syzkaller.appspot.com/bug?extid=9b260fc33297966f5a8e
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=174272b2900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9b260fc33297966f5a8e@syzkaller.appspotmail.com

I think the below should fix it, for this use case and potentially others.
If the ring is closed and the task_work bound req is holding the last
reference, we need to hold a ctx reference around it.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5488698189da..cc4bb16ff570 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1821,8 +1821,10 @@ static void __io_req_task_submit(struct io_kiocb *req)
 static void io_req_task_submit(struct callback_head *cb)
 {
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct io_ring_ctx *ctx = req->ctx;
 
 	__io_req_task_submit(req);
+	percpu_ref_put(&ctx->refs);
 }
 
 static void io_req_task_queue(struct io_kiocb *req)
@@ -1830,6 +1832,7 @@ static void io_req_task_queue(struct io_kiocb *req)
 	int ret;
 
 	init_task_work(&req->task_work, io_req_task_submit);
+	percpu_ref_get(&req->ctx->refs);
 
 	ret = io_req_task_work_add(req, &req->task_work);
 	if (unlikely(ret)) {
@@ -2318,6 +2321,8 @@ static void io_rw_resubmit(struct callback_head *cb)
 		refcount_inc(&req->refs);
 		io_queue_async_work(req);
 	}
+
+	percpu_ref_put(&ctx->refs);
 }
 #endif
 
@@ -2330,6 +2335,8 @@ static bool io_rw_reissue(struct io_kiocb *req, long res)
 		return false;
 
 	init_task_work(&req->task_work, io_rw_resubmit);
+	percpu_ref_get(&req->ctx->refs);
+
 	ret = io_req_task_work_add(req, &req->task_work);
 	if (!ret)
 		return true;
@@ -3033,6 +3040,8 @@ static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
 	list_del_init(&wait->entry);
 
 	init_task_work(&req->task_work, io_req_task_submit);
+	percpu_ref_get(&req->ctx->refs);
+
 	/* submit ref gets dropped, acquire a new one */
 	refcount_inc(&req->refs);
 	ret = io_req_task_work_add(req, &req->task_work);
@@ -4565,6 +4574,8 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
 
 	req->result = mask;
 	init_task_work(&req->task_work, func);
+	percpu_ref_get(&req->ctx->refs);
+
 	/*
 	 * If this fails, then the task is exiting. When a task exits, the
 	 * work gets canceled, so just cancel this request as well instead
@@ -4652,11 +4663,13 @@ static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)
 static void io_poll_task_func(struct callback_head *cb)
 {
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct io_ring_ctx *ctx = req->ctx;
 	struct io_kiocb *nxt = NULL;
 
 	io_poll_task_handler(req, &nxt);
 	if (nxt)
 		__io_req_task_submit(nxt);
+	percpu_ref_put(&ctx->refs);
 }
 
 static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
@@ -4752,6 +4765,7 @@ static void io_async_task_func(struct callback_head *cb)
 
 	if (io_poll_rewait(req, &apoll->poll)) {
 		spin_unlock_irq(&ctx->completion_lock);
+		percpu_ref_put(&ctx->refs);
 		return;
 	}
 

-- 
Jens Axboe