[PATCH v3 4/4] samples/landlock: Add LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS to sampler

[Justin Suess <utilityemal77@gmail.com>]

Add LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS to the default flag setting.
Gate the flag on the ABI version, but do not expose any userspace
control over this flag as it has no practical effect on the resulting
sandbox.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---

Notes:
    v2->v3:
    - New patch: use LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS by default in the
      sandboxer, gated on the ABI version, with a prctl fallback

 samples/landlock/sandboxer.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index ac71019e6212..030583273f3f 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -369,7 +369,7 @@ static int add_quiet_access(const char *const env_var,
 	return 0;
 }
 
-#define LANDLOCK_ABI_LAST 10
+#define LANDLOCK_ABI_LAST 11
 
 #define XSTR(s) #s
 #define STR(s) XSTR(s)
@@ -453,8 +453,9 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		.quiet_scoped = 0,
 	};
 	bool quiet_supported = true;
-	int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
-	int set_restrict_flags = 0;
+	int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON |
+				       LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+	int set_restrict_flags = LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
 
 	if (argc < 2) {
 		fprintf(stderr, help, argv[0]);
@@ -545,6 +546,12 @@ int main(const int argc, char *const argv[], char *const *const envp)
 			  LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP);
 		/* Removes quiet flags for ABI < 10 later on. */
 		quiet_supported = false;
+		__attribute__((fallthrough));
+	case 10:
+		/* Removes LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS for ABI < 11 */
+		supported_restrict_flags &=
+			~LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
+		set_restrict_flags &= ~LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS;
 
 		/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
 		fprintf(stderr,
@@ -673,7 +680,8 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		}
 	}
 
-	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+	if (!(set_restrict_flags & LANDLOCK_RESTRICT_SELF_NO_NEW_PRIVS) &&
+	    prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
 		perror("Failed to restrict privileges");
 		goto err_close_ruleset;
 	}
-- 
2.54.0