[PATCH 7.1 004/228] selinux: do not cancel a policy conversion that never started

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bryam Vargas <[email protected]>

commit e5c0235a3c4e9eb047a16cd02323fe4ecf2f570e upstream.

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.

Cc: [email protected]
Fixes: 02a52c5c8c3b ("selinux: move policy commit after updating selinuxfs")
Signed-off-by: Bryam Vargas <[email protected]>
Acked-by: Stephen Smalley <[email protected]>
Signed-off-by: Paul Moore <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 security/selinux/ss/services.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2220,7 +2220,9 @@ void selinux_policy_cancel(struct selinu
 	oldpolicy = rcu_dereference_protected(state->policy,
 					lockdep_is_held(&state->policy_mutex));
 
-	sidtab_cancel_convert(oldpolicy->sidtab);
+	/* a first load has no outgoing policy and converted nothing */
+	if (oldpolicy)
+		sidtab_cancel_convert(oldpolicy->sidtab);
 	selinux_policy_free(load_state->policy);
 	kfree(load_state->convert_data);
 }