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Date:   Thu, 12 Jan 2023 07:24:43 -0800
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Subject: Re: [syzbot] KASAN: use-after-free Read in io_fallback_req_func
From:   syzbot <syzbot+bc022c162e3b001bf607@syzkaller.appspotmail.com>
To:     asml.silence@gmail.com, axboe@kernel.dk, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
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syzbot has found a reproducer for the following issue on:

HEAD commit:    0a093b2893c7 Add linux-next specific files for 20230112
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=176167ba480000
kernel config:  https://syzkaller.appspot.com/x/.config?x=835f3591019836d5
dashboard link: https://syzkaller.appspot.com/bug?extid=bc022c162e3b001bf607
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d58fbe480000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=151b0316480000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8111a570d6cb/disk-0a093b28.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ecc135b7fc9a/vmlinux-0a093b28.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ca8d73b446ea/bzImage-0a093b28.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bc022c162e3b001bf607@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in io_fallback_req_func+0xc7/0x204 io_uring/io_uring.c:251
Read of size 8 at addr ffff8880793aa948 by task kworker/0:3/4401

CPU: 0 PID: 4401 Comm: kworker/0:3 Not tainted 6.2.0-rc3-next-20230112-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: events io_fallback_req_func
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:306 [inline]
 print_report+0x15e/0x45d mm/kasan/report.c:417
 kasan_report+0xc0/0xf0 mm/kasan/report.c:517
 io_fallback_req_func+0xc7/0x204 io_uring/io_uring.c:251
 process_one_work+0x9bf/0x1750 kernel/workqueue.c:2293
 worker_thread+0x669/0x1090 kernel/workqueue.c:2440
 kthread+0x2e8/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
 </TASK>

Allocated by task 5077:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 __kasan_slab_alloc+0x7f/0x90 mm/kasan/common.c:325
 kasan_slab_alloc include/linux/kasan.h:186 [inline]
 slab_post_alloc_hook mm/slab.h:769 [inline]
 kmem_cache_alloc_bulk+0x3aa/0x730 mm/slub.c:4033
 __io_alloc_req_refill+0xcc/0x40b io_uring/io_uring.c:1062
 io_alloc_req_refill io_uring/io_uring.h:348 [inline]
 io_submit_sqes.cold+0x7c/0xc2 io_uring/io_uring.c:2407
 __do_sys_io_uring_enter+0x9e4/0x2c10 io_uring/io_uring.c:3429
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 31:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x160/0x1c0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:162 [inline]
 slab_free_hook mm/slub.c:1781 [inline]
 slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1807
 slab_free mm/slub.c:3787 [inline]
 kmem_cache_free+0xec/0x4e0 mm/slub.c:3809
 io_req_caches_free+0x1a9/0x1e6 io_uring/io_uring.c:2737
 io_ring_exit_work+0x2e7/0xc80 io_uring/io_uring.c:2967
 process_one_work+0x9bf/0x1750 kernel/workqueue.c:2293
 worker_thread+0x669/0x1090 kernel/workqueue.c:2440
 kthread+0x2e8/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

The buggy address belongs to the object at ffff8880793aa8c0
 which belongs to the cache io_kiocb of size 216
The buggy address is located 136 bytes inside of
 216-byte region [ffff8880793aa8c0, ffff8880793aa998)

The buggy address belongs to the physical page:
page:ffffea0001e4ea80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x793aa
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 ffff88814610fc80 dead000000000122 0000000000000000
raw: 0000000000000000 00000000800c000c 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 5077, tgid 5077 (syz-executor134), ts 60034717602, free_ts 59988620363
 prep_new_page mm/page_alloc.c:2549 [inline]
 get_page_from_freelist+0x11bb/0x2d50 mm/page_alloc.c:4324
 __alloc_pages+0x1cb/0x5c0 mm/page_alloc.c:5590
 alloc_pages+0x1aa/0x270 mm/mempolicy.c:2281
 alloc_slab_page mm/slub.c:1851 [inline]
 allocate_slab+0x25f/0x350 mm/slub.c:1998
 new_slab mm/slub.c:2051 [inline]
 ___slab_alloc+0xa91/0x1400 mm/slub.c:3193
 __kmem_cache_alloc_bulk mm/slub.c:3951 [inline]
 kmem_cache_alloc_bulk+0x23d/0x730 mm/slub.c:4026
 __io_alloc_req_refill+0xcc/0x40b io_uring/io_uring.c:1062
 io_alloc_req_refill io_uring/io_uring.h:348 [inline]
 io_submit_sqes.cold+0x7c/0xc2 io_uring/io_uring.c:2407
 __do_sys_io_uring_enter+0x9e4/0x2c10 io_uring/io_uring.c:3429
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1451 [inline]
 free_pcp_prepare+0x4d0/0x910 mm/page_alloc.c:1501
 free_unref_page_prepare mm/page_alloc.c:3387 [inline]
 free_unref_page_list+0x176/0xcd0 mm/page_alloc.c:3528
 release_pages+0xcb1/0x1330 mm/swap.c:1072
 tlb_batch_pages_flush+0xa8/0x1a0 mm/mmu_gather.c:97
 tlb_flush_mmu_free mm/mmu_gather.c:292 [inline]
 tlb_flush_mmu mm/mmu_gather.c:299 [inline]
 tlb_finish_mmu+0x14b/0x7e0 mm/mmu_gather.c:391
 exit_mmap+0x202/0x7c0 mm/mmap.c:3100
 __mmput+0x128/0x4c0 kernel/fork.c:1212
 mmput+0x60/0x70 kernel/fork.c:1234
 exit_mm kernel/exit.c:563 [inline]
 do_exit+0x9ac/0x2a90 kernel/exit.c:854
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
 get_signal+0x225f/0x24f0 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x11f/0x240 kernel/entry/common.c:204
 irqentry_exit_to_user_mode+0x9/0x40 kernel/entry/common.c:310
 exc_page_fault+0xc0/0x170 arch/x86/mm/fault.c:1557
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570

Memory state around the buggy address:
 ffff8880793aa800: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
 ffff8880793aa880: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>ffff8880793aa900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8880793aa980: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880793aaa00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================