[PATCH] libsepol/cil: handle SID without assigned context when writing policy.conf

["Christian Göttsche" <cgzones@googlemail.com>]

CIL permits not assigning a context to a SID, e.g. to an unused initial
SID, e.g. 'any_socket'.

When using the example policy from the SELinux Notebook,
https://github.com/SELinuxProject/selinux-notebook/blob/main/src/notebook-examples/cil-policy/cil-policy.cil,
secilc logs:

    No context assigned to SID any_socket, omitting from policy at cil-policy.cil:166

But secil2conf segfaults when writing the policy.conf:

    ../cil/src/cil_policy.c:274:2: runtime error: member access within null pointer of type 'struct cil_context'

Only print the assigned context if actually available.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
 libsepol/cil/src/cil_policy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libsepol/cil/src/cil_policy.c b/libsepol/cil/src/cil_policy.c
index 30d507f1..863636c7 100644
--- a/libsepol/cil/src/cil_policy.c
+++ b/libsepol/cil/src/cil_policy.c
@@ -1661,7 +1661,9 @@ static void cil_sid_contexts_to_policy(FILE *out, struct cil_list *sids, int mls
 	cil_list_for_each(i1, sids) {
 		sid = i1->data;
 		fprintf(out, "sid %s ", sid->datum.fqn);
-		cil_context_to_policy(out, sid->context, mls);
+		if (sid->context) {
+			cil_context_to_policy(out, sid->context, mls);
+		}
 		fprintf(out,"\n");
 	}
 }
-- 
2.30.1