In the Linux kernel, the following vulnerability has been resolved:
selinux: do not cancel a policy conversion that never started
sel_write_load() calls selinux_policy_cancel() when sel_make_policy_nodes()
fails, and that helper dereferences the outgoing policy to cancel its
sidtab conversion. On the first policy load there is no outgoing policy:
security_load_policy() returns early for that case, before it converts
anything, and state->policy is still NULL. A first load that fails while
building the selinuxfs tree therefore takes a NULL dereference in
selinux_policy_cancel(), reached from a write(2) to /sys/fs/selinux/load.
Skip the cancel when there is no old policy, mirroring the check
security_load_policy() already makes before it converts.
