Date:   Fri, 29 Oct 2021 15:46:34 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     syzbot <syzbot+78b76ebc91042904f34e@...kaller.appspotmail.com>,
        axboe@...nel.dk, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Write in __io_free_req

On 10/29/21 15:34, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    bdcc9f6a5682 Add linux-next specific files for 20211029
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a87e22b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cea91ee10b0cd274
> dashboard link: https://syzkaller.appspot.com/bug?extid=78b76ebc91042904f34e
> 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=10cf03e2b00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+78b76ebc91042904f34e@...kaller.appspotmail.com

#syz test: git://git.kernel.dk/linux-block 3884b83dff245e41def99ceacca8ed2056baf0a8

> 
> ==================================================================
> BUG: KASAN: use-after-free in wq_list_add_head fs/io-wq.h:71 [inline]
> BUG: KASAN: use-after-free in __io_free_req+0x33f/0x3c5 fs/io_uring.c:2040
> Write of size 8 at addr ffff8880713ecbb8 by task syz-executor.0/8059
> 
> CPU: 1 PID: 8059 Comm: syz-executor.0 Not tainted 5.15.0-rc7-next-20211029-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>   print_address_description.constprop.0.cold+0x8d/0x320 mm/kasan/report.c:247
>   __kasan_report mm/kasan/report.c:433 [inline]
>   kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
>   wq_list_add_head fs/io-wq.h:71 [inline]
>   __io_free_req+0x33f/0x3c5 fs/io_uring.c:2040
>   tctx_task_work+0x1b3/0x630 fs/io_uring.c:2207
>   task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>   exit_task_work include/linux/task_work.h:32 [inline]
>   do_exit+0xc14/0x2b40 kernel/exit.c:832
>   do_group_exit+0x125/0x310 kernel/exit.c:929
>   get_signal+0x47d/0x21d0 kernel/signal.c:2820
>   arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868
>   handle_signal_work kernel/entry/common.c:148 [inline]
>   exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>   exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207
>   __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
>   syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
>   do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f9da8c4ea39
> Code: Unable to access opcode bytes at RIP 0x7f9da8c4ea0f.
> RSP: 002b:00007f9da83a3218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: fffffffffffffe00 RBX: 00007f9da8d62028 RCX: 00007f9da8c4ea39
> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f9da8d62028
> RBP: 00007f9da8d62020 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9da8d6202c
> R13: 00007ffd6e91741f R14: 00007f9da83a3300 R15: 0000000000022000
>   </TASK>
> 
> Allocated by task 8059:
>   kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
>   kasan_set_track mm/kasan/common.c:46 [inline]
>   set_alloc_info mm/kasan/common.c:434 [inline]
>   __kasan_slab_alloc+0x90/0xc0 mm/kasan/common.c:467
>   kasan_slab_alloc include/linux/kasan.h:259 [inline]
>   slab_post_alloc_hook mm/slab.h:519 [inline]
>   kmem_cache_alloc_bulk+0x39d/0x720 mm/slub.c:3730
>   __io_alloc_req_refill fs/io_uring.c:1977 [inline]
>   io_alloc_req_refill fs/io_uring.c:2003 [inline]
>   io_submit_sqes.cold+0x20b/0x43d fs/io_uring.c:7325
>   __do_sys_io_uring_enter+0xf6e/0x1f50 fs/io_uring.c:10052
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Freed by task 1041:
>   kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
>   kasan_set_track+0x21/0x30 mm/kasan/common.c:46
>   kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
>   ____kasan_slab_free mm/kasan/common.c:366 [inline]
>   ____kasan_slab_free mm/kasan/common.c:328 [inline]
>   __kasan_slab_free+0xff/0x130 mm/kasan/common.c:374
>   kasan_slab_free include/linux/kasan.h:235 [inline]
>   slab_free_hook mm/slub.c:1723 [inline]
>   slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1749
>   slab_free mm/slub.c:3513 [inline]
>   kmem_cache_free+0x92/0x5e0 mm/slub.c:3529
>   io_req_caches_free+0x1aa/0x1e6 fs/io_uring.c:9291
>   io_ring_exit_work+0x1e4/0xbe8 fs/io_uring.c:9467
>   process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
>   worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
>   kthread+0x405/0x4f0 kernel/kthread.c:327
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> 
> The buggy address belongs to the object at ffff8880713ecb40
>   which belongs to the cache io_kiocb of size 224
> The buggy address is located 120 bytes inside of
>   224-byte region [ffff8880713ecb40, ffff8880713ecc20)
> The buggy address belongs to the page:
> page:ffffea0001c4fb00 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880713ec8c0 pfn:0x713ec
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 ffffea0001c4d400 dead000000000004 ffff88814607bdc0
> raw: ffff8880713ec8c0 00000000800c000b 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 7168, ts 1580559391621, free_ts 1580537948913
>   prep_new_page mm/page_alloc.c:2418 [inline]
>   get_page_from_freelist+0xa72/0x2f50 mm/page_alloc.c:4149
>   __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5369
>   alloc_pages+0x1a7/0x300 mm/mempolicy.c:2191
>   alloc_slab_page mm/slub.c:1793 [inline]
>   allocate_slab mm/slub.c:1930 [inline]
>   new_slab+0x32d/0x4a0 mm/slub.c:1993
>   ___slab_alloc+0x918/0xfe0 mm/slub.c:3022
>   kmem_cache_alloc_bulk+0x21a/0x720 mm/slub.c:3706
>   __io_alloc_req_refill fs/io_uring.c:1977 [inline]
>   io_alloc_req_refill fs/io_uring.c:2003 [inline]
>   io_submit_sqes.cold+0x20b/0x43d fs/io_uring.c:7325
>   __do_sys_io_uring_enter+0xf6e/0x1f50 fs/io_uring.c:10052
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> page last free stack trace:
>   reset_page_owner include/linux/page_owner.h:24 [inline]
>   free_pages_prepare mm/page_alloc.c:1338 [inline]
>   free_pcp_prepare+0x374/0x870 mm/page_alloc.c:1389
>   free_unref_page_prepare mm/page_alloc.c:3309 [inline]
>   free_unref_page_list+0x1a9/0xfa0 mm/page_alloc.c:3425
>   release_pages+0x3f4/0x1480 mm/swap.c:979
>   tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
>   tlb_flush_mmu_free mm/mmu_gather.c:242 [inline]
>   tlb_flush_mmu mm/mmu_gather.c:249 [inline]
>   tlb_finish_mmu+0x165/0x8c0 mm/mmu_gather.c:340
>   exit_mmap+0x1ea/0x630 mm/mmap.c:3173
>   __mmput+0x122/0x4b0 kernel/fork.c:1164
>   mmput+0x56/0x60 kernel/fork.c:1185
>   exit_mm kernel/exit.c:507 [inline]
>   do_exit+0xb27/0x2b40 kernel/exit.c:819
>   do_group_exit+0x125/0x310 kernel/exit.c:929
>   get_signal+0x47d/0x21d0 kernel/signal.c:2820
>   arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868
>   handle_signal_work kernel/entry/common.c:148 [inline]
>   exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>   exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207
>   __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
>   syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
>   do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Memory state around the buggy address:
>   ffff8880713eca80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>   ffff8880713ecb00: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>> ffff8880713ecb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                          ^
>   ffff8880713ecc00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
>   ffff8880713ecc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

-- 
Pavel Begunkov

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