kernel: null-ptr-dereference bug in btrfs_rm_device in fs/btrfs/volumes.c References: https://lore.kernel.org/linux-btrfs/CAFcO6XO5TC5sEo-C9JGC75JkNAzkOSSLA3a=bwQqXFFbRTZ7Gw@mail.gmail.com/T/#md4b850f33616b7364f86e6fed144abc925f3669c https://lore.kernel.org/linux-btrfs/20210806102415.304717-1-wqu@suse.com/T/#u CREATE(Triage):(User=admin) CVE-2021-3739 (https://nvd.nist.gov/vuln/detail/CVE-2021-3739)
