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Fix get_zfs_sb race with concurrent umount
Certain ioctl operations will call get_zfs_sb, which will holds an active count on sb without checking whether it's active or not. This will result in use-after-free. We fix this by using atomic_inc_not_zero to make sure we got an active sb. P1 P2 --- --- deactivate_locked_super(): s_active = 0 zfs_sb_hold() ->get_zfs_sb(): s_active = 1 ->zpl_kill_sb() -->zpl_put_super() --->zfs_umount() ---->zfs_sb_free(zsb) zfs_sb_rele(zsb) Signed-off-by: Chunwei Chen <[email protected]>
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