Date:   Thu, 12 Jan 2023 10:38:04 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     syzbot <syzbot+131f71f381afff1eaa35@...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 Read in io_req_caches_free

On 1/12/23 10:26, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0a093b2893c7 Add linux-next specific files for 20230112
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1605ee86480000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=835f3591019836d5
> dashboard link: https://syzkaller.appspot.com/bug?extid=131f71f381afff1eaa35
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.

#syz test: git://git.kernel.dk/linux.git syztest

> 
> 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+131f71f381afff1eaa35@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in wq_stack_extract io_uring/slist.h:126 [inline]
> BUG: KASAN: use-after-free in io_alloc_req io_uring/io_uring.h:356 [inline]
> BUG: KASAN: use-after-free in io_req_caches_free+0x18d/0x1e6 io_uring/io_uring.c:2735
> Read of size 8 at addr ffff8880263397f8 by task kworker/u4:9/5456
> 
> CPU: 0 PID: 5456 Comm: kworker/u4:9 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_unbound io_ring_exit_work
> 
> 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
>   wq_stack_extract io_uring/slist.h:126 [inline]
>   io_alloc_req io_uring/io_uring.h:356 [inline]
>   io_req_caches_free+0x18d/0x1e6 io_uring/io_uring.c:2735
>   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
>   </TASK>
> 
> Allocated by task 6234:
>   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 5456:
>   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 ffff888026339780
>   which belongs to the cache io_kiocb of size 216
> The buggy address is located 120 bytes inside of
>   216-byte region [ffff888026339780, ffff888026339858)
> 
> The buggy address belongs to the physical page:
> page:ffffea000098ce40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x26339
> memcg:ffff888026d5d401
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 ffff8881461f8a00 ffffea0001c18840 0000000000000006
> raw: 0000000000000000 00000000000c000c 00000001ffffffff ffff888026d5d401
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 5955, tgid 5954 (syz-executor.2), ts 292007873728, free_ts 283379272604
>   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+0x1d/0x490 mm/page_alloc.c:3482
>   relay_destroy_buf+0x121/0x3e0 kernel/relay.c:201
>   relay_remove_buf kernel/relay.c:221 [inline]
>   kref_put include/linux/kref.h:65 [inline]
>   relay_close_buf+0x153/0x1b0 kernel/relay.c:430
>   relay_close kernel/relay.c:766 [inline]
>   relay_close+0x3a4/0x590 kernel/relay.c:752
>   blk_trace_free+0x37/0x190 kernel/trace/blktrace.c:316
>   blk_trace_cleanup kernel/trace/blktrace.c:384 [inline]
>   __blk_trace_remove+0x83/0x190 kernel/trace/blktrace.c:397
>   blk_trace_ioctl+0x24c/0x290 kernel/trace/blktrace.c:760
>   blkdev_common_ioctl+0x11c7/0x1ba0 block/ioctl.c:536
>   blkdev_ioctl+0x2c6/0x800 block/ioctl.c:610
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:870 [inline]
>   __se_sys_ioctl fs/ioctl.c:856 [inline]
>   __x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
>   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
> 
> Memory state around the buggy address:
>   ffff888026339680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   ffff888026339700: 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff888026339780: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                                  ^
>   ffff888026339800: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
>   ffff888026339880: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
> ==================================================================
> 
> 
> ---
> 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.

-- 
Pavel Begunkov

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