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Date:   Sat, 28 Nov 2020 09:19:21 -0800
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Subject: Re: KASAN: use-after-free Read in idr_for_each (2)
From:   syzbot <syzbot+12056a09a0311d758e60@syzkaller.appspotmail.com>
To:     axboe@kernel.dk, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk
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syzbot has found a reproducer for the following issue on:

HEAD commit:    c84e1efa Merge tag 'asm-generic-fixes-5.10-2' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1251d759500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cb8d1a3819ba4356
dashboard link: https://syzkaller.appspot.com/bug?extid=12056a09a0311d758e60
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1126cce9500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1173d2e9500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+12056a09a0311d758e60@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in radix_tree_next_slot include/linux/radix-tree.h:422 [inline]
BUG: KASAN: use-after-free in idr_for_each+0x206/0x220 lib/idr.c:202
Read of size 8 at addr ffff888032eb2c40 by task kworker/u4:4/186

CPU: 1 PID: 186 Comm: kworker/u4:4 Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound io_ring_exit_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 radix_tree_next_slot include/linux/radix-tree.h:422 [inline]
 idr_for_each+0x206/0x220 lib/idr.c:202
 io_destroy_buffers fs/io_uring.c:8275 [inline]
 io_ring_ctx_free fs/io_uring.c:8298 [inline]
 io_ring_exit_work+0x3f7/0x7a0 fs/io_uring.c:8375
 process_one_work+0x933/0x15a0 kernel/workqueue.c:2272
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2418
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Allocated by task 10961:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:461
 slab_post_alloc_hook mm/slab.h:526 [inline]
 slab_alloc_node mm/slub.c:2891 [inline]
 slab_alloc mm/slub.c:2899 [inline]
 kmem_cache_alloc+0x122/0x460 mm/slub.c:2904
 radix_tree_node_alloc.constprop.0+0x7c/0x350 lib/radix-tree.c:274
 idr_get_free+0x4c5/0x940 lib/radix-tree.c:1504
 idr_alloc_u32+0x170/0x2d0 lib/idr.c:46
 idr_alloc+0xc2/0x130 lib/idr.c:87
 io_provide_buffers fs/io_uring.c:4032 [inline]
 io_issue_sqe+0x2fc4/0x3d10 fs/io_uring.c:6012
 __io_queue_sqe+0x132/0xda0 fs/io_uring.c:6232
 io_queue_sqe+0x623/0x11f0 fs/io_uring.c:6298
 io_submit_sqe fs/io_uring.c:6367 [inline]
 io_submit_sqes+0x15e1/0x28a0 fs/io_uring.c:6596
 __do_sys_io_uring_enter+0xc90/0x1ab0 fs/io_uring.c:8983
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 8546:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
 kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
 __kasan_slab_free+0x102/0x140 mm/kasan/common.c:422
 slab_free_hook mm/slub.c:1544 [inline]
 slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1577
 slab_free mm/slub.c:3142 [inline]
 kmem_cache_free+0x82/0x350 mm/slub.c:3158
 rcu_do_batch kernel/rcu/tree.c:2476 [inline]
 rcu_core+0x5df/0xe80 kernel/rcu/tree.c:2711
 __do_softirq+0x2a0/0x9f6 kernel/softirq.c:298

Last call_rcu():
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_record_aux_stack+0xc0/0xf0 mm/kasan/generic.c:346
 __call_rcu kernel/rcu/tree.c:2953 [inline]
 call_rcu+0xbb/0x700 kernel/rcu/tree.c:3027
 radix_tree_node_free lib/radix-tree.c:308 [inline]
 delete_node+0x591/0x8c0 lib/radix-tree.c:571
 __radix_tree_delete+0x190/0x370 lib/radix-tree.c:1377
 radix_tree_delete_item+0xe7/0x230 lib/radix-tree.c:1428
 __io_remove_buffers fs/io_uring.c:3930 [inline]
 __io_remove_buffers fs/io_uring.c:3909 [inline]
 __io_destroy_buffers+0x161/0x200 fs/io_uring.c:8269
 idr_for_each+0x113/0x220 lib/idr.c:208
 io_destroy_buffers fs/io_uring.c:8275 [inline]
 io_ring_ctx_free fs/io_uring.c:8298 [inline]
 io_ring_exit_work+0x3f7/0x7a0 fs/io_uring.c:8375
 process_one_work+0x933/0x15a0 kernel/workqueue.c:2272
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2418
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

The buggy address belongs to the object at ffff888032eb2c00
 which belongs to the cache radix_tree_node of size 576
The buggy address is located 64 bytes inside of
 576-byte region [ffff888032eb2c00, ffff888032eb2e40)
The buggy address belongs to the page:
page:00000000102f3139 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x32eb0
head:00000000102f3139 order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff88801004db40
raw: 0000000000000000 0000000000170017 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888032eb2b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888032eb2b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888032eb2c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff888032eb2c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888032eb2d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================