• Dan Williams's avatar
    block: fix del_gendisk() vs blkdev_ioctl crash · 6ddbac9a
    Dan Williams authored
    commit ac34f15e upstream.
    When tearing down a block device early in its lifetime, userspace may
    still be performing discovery actions like blkdev_ioctl() to re-read
    The nvdimm_revalidate_disk() implementation depends on
    disk->driverfs_dev to be valid at entry.  However, it is set to NULL in
    del_gendisk() and fatally this is happening *before* the disk device is
    deleted from userspace view.
    There's no reason for del_gendisk() to clear ->driverfs_dev.  That
    device is the parent of the disk.  It is guaranteed to not be freed
    until the disk, as a child, drops its ->parent reference.
    We could also fix this issue locally in nvdimm_revalidate_disk() by
    using disk_to_dev(disk)->parent, but lets fix it globally since
    ->driverfs_dev follows the lifetime of the parent.  Longer term we
    should probably just add a @parent parameter to add_disk(), and stop
    carrying this pointer in the gendisk.
     BUG: unable to handle kernel NULL pointer dereference at           (null)
     IP: [<ffffffffa00340a8>] nvdimm_revalidate_disk+0x18/0x90 [libnvdimm]
     CPU: 2 PID: 538 Comm: systemd-udevd Tainted: G           O    4.4.0-rc5 #2257
     Call Trace:
      [<ffffffff8143e5c7>] rescan_partitions+0x87/0x2c0
      [<ffffffff810f37f9>] ? __lock_is_held+0x49/0x70
      [<ffffffff81438c62>] __blkdev_reread_part+0x72/0xb0
      [<ffffffff81438cc5>] blkdev_reread_part+0x25/0x40
      [<ffffffff8143982d>] blkdev_ioctl+0x4fd/0x9c0
      [<ffffffff811246c9>] ? current_kernel_time64+0x69/0xd0
      [<ffffffff812916dd>] block_ioctl+0x3d/0x50
      [<ffffffff81264c38>] do_vfs_ioctl+0x308/0x560
      [<ffffffff8115dbd1>] ? __audit_syscall_entry+0xb1/0x100
      [<ffffffff810031d6>] ? do_audit_syscall_entry+0x66/0x70
      [<ffffffff81264f09>] SyS_ioctl+0x79/0x90
      [<ffffffff81902672>] entry_SYSCALL_64_fastpath+0x12/0x76
    Cc: Jan Kara <jack@suse.cz>
    Cc: Jens Axboe <axboe@fb.com>
    Reported-by: default avatarRobert Hu <robert.hu@intel.com>
    Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
genhd.c 44.4 KB