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SubjectRe: KASAN: use-after-free Read in blk_mq_free_rqs
Hello,

Thanks for your report!

On Fri, Jun 7, 2019 at 4:16 AM syzbot
<syzbot+784281a934c3f71eb71a@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 9221dced Merge tag 'for-linus-20190601' of git://git.kerne..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16b3b772a00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=1fa7e451a5cac069
> dashboard link: https://syzkaller.appspot.com/bug?extid=784281a934c3f71eb71a
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=149089aaa00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11b24edea00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+784281a934c3f71eb71a@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in blk_mq_free_rqs+0x49f/0x4b0
> block/blk-mq.c:2049
> Read of size 8 at addr ffff88809b5c0b10 by task kworker/1:1/22
>
> CPU: 1 PID: 22 Comm: kworker/1:1 Not tainted 5.2.0-rc2+ #17
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: events __blk_release_queue
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x172/0x1f0 lib/dump_stack.c:113
> print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
> __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
> kasan_report+0x12/0x20 mm/kasan/common.c:614
> __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
> blk_mq_free_rqs+0x49f/0x4b0 block/blk-mq.c:2049
> blk_mq_sched_free_tags block/blk-mq-sched.c:453 [inline]
> blk_mq_sched_tags_teardown+0x126/0x210 block/blk-mq-sched.c:485
> blk_mq_exit_sched+0x1fa/0x2d0 block/blk-mq-sched.c:557
> elevator_exit+0x70/0xa0 block/elevator.c:185
> blk_exit_queue block/blk-sysfs.c:853 [inline]
> __blk_release_queue+0x127/0x330 block/blk-sysfs.c:895
> process_one_work+0x989/0x1790 kernel/workqueue.c:2269
> worker_thread+0x98/0xe40 kernel/workqueue.c:2415
> kthread+0x354/0x420 kernel/kthread.c:255
> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
>
> Allocated by task 8904:
> save_stack+0x23/0x90 mm/kasan/common.c:71
> set_track mm/kasan/common.c:79 [inline]
> __kasan_kmalloc mm/kasan/common.c:489 [inline]
> __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
> kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
> kmem_cache_alloc_trace+0x151/0x750 mm/slab.c:3555
> kmalloc include/linux/slab.h:547 [inline]
> kzalloc include/linux/slab.h:742 [inline]
> loop_add+0x51/0x8d0 drivers/block/loop.c:1973
> loop_control_ioctl drivers/block/loop.c:2157 [inline]
> loop_control_ioctl+0x165/0x360 drivers/block/loop.c:2139
> vfs_ioctl fs/ioctl.c:46 [inline]
> file_ioctl fs/ioctl.c:509 [inline]
> do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
> ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
> __do_sys_ioctl fs/ioctl.c:720 [inline]
> __se_sys_ioctl fs/ioctl.c:718 [inline]
> __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 8905:
> save_stack+0x23/0x90 mm/kasan/common.c:71
> set_track mm/kasan/common.c:79 [inline]
> __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
> kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
> __cache_free mm/slab.c:3432 [inline]
> kfree+0xcf/0x220 mm/slab.c:3755
> loop_remove+0xa1/0xd0 drivers/block/loop.c:2078
> loop_control_ioctl drivers/block/loop.c:2173 [inline]
> loop_control_ioctl+0x320/0x360 drivers/block/loop.c:2139
> vfs_ioctl fs/ioctl.c:46 [inline]
> file_ioctl fs/ioctl.c:509 [inline]
> do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
> ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
> __do_sys_ioctl fs/ioctl.c:720 [inline]
> __se_sys_ioctl fs/ioctl.c:718 [inline]
> __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff88809b5c0900
> which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 528 bytes inside of
> 1024-byte region [ffff88809b5c0900, ffff88809b5c0d00)
> The buggy address belongs to the page:
> page:ffffea00026d7000 refcount:1 mapcount:0 mapping:ffff8880aa400ac0
> index:0x0 compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea0002411188 ffffea000290c088 ffff8880aa400ac0
> raw: 0000000000000000 ffff88809b5c0000 0000000100000007 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff88809b5c0a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809b5c0a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff88809b5c0b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff88809b5c0b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809b5c0c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

It should be fixed by the following patch:

https://lore.kernel.org/linux-block/20190606144714.GA6549@t480-pf1aa2c2/T/#m0a3d000613bcfd5271a0748ff230a4eccb2d65f1

Thanks,
Ming Lei

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