[PATCH 1/4] selinux: do not cancel a policy conversion that never started

[Bryam Vargas via B4 Relay]

From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

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.

Fixes: 02a52c5c8c3b ("selinux: move policy commit after updating selinuxfs")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
---
 security/selinux/ss/services.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 2d828548f3db..90e81186cb2e 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2221,7 +2221,9 @@ void selinux_policy_cancel(struct selinux_load_state *load_state)
 	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);
 }

-- 
2.55.0