[pseudo,3/6] ports/linux/pseudo_wrappers: Report Landlock as unsupported

diff --git a/README.security b/README.security
index 45533f2..11b9b4b 100644
--- a/README.security
+++ b/README.security
@@ -141,6 +141,20 @@  that user.  The resulting metadata can only be trusted as much as every
 process running as the build user.
 
 
+7. SELF-SANDBOXING IS DISABLED
+
+libpseudo has to keep reaching the server and the filesystem on behalf
+of the program it is loaded into, so pseudo turns off the ways a
+program can restrict itself (ports/linux/pseudo_wrappers.c).  Requests
+to install a seccomp filter through syscall() or prctl() report success
+without installing anything, and the Landlock system calls fail with
+ENOSYS, as if the kernel did not support Landlock.  A program that
+sandboxes itself, such as xz, runs unsandboxed under pseudo, and one
+that refuses to run without its sandbox fails.  This doesn't apply to
+programs pseudo does not intercept (see section 1), and the Landlock
+calls reach the kernel while PSEUDO_DISABLED is set.
+
+
 RECOMMENDATIONS:
 
 * Run pseudo only on build output that is private to the build and is
diff --git a/ports/linux/pseudo_wrappers.c b/ports/linux/pseudo_wrappers.c
index 5e26aff..7d1e7d9 100644
--- a/ports/linux/pseudo_wrappers.c
+++ b/ports/linux/pseudo_wrappers.c
@@ -77,6 +77,11 @@  syscall(long number, ...) {
 #ifdef SYS_seccomp
 	    && number != SYS_seccomp
 #endif
+#ifdef SYS_landlock_create_ruleset
+	    && number != SYS_landlock_create_ruleset
+	    && number != SYS_landlock_add_rule
+	    && number != SYS_landlock_restrict_self
+#endif
 	    ) {
 		if (!real_syscall)
 			real_syscall = (long (*)(long, ...)) dlsym(RTLD_NEXT, "syscall");
@@ -109,6 +114,19 @@  syscall(long number, ...) {
                 goto call_syscall;
         }
 
+#ifdef SYS_landlock_create_ruleset
+	/* A Landlock sandbox also binds libpseudo, which then can't reach the
+	 * server (YOCTO #16493), so report Landlock as unsupported.
+	 */
+	if (number == SYS_landlock_create_ruleset ||
+	    number == SYS_landlock_add_rule ||
+	    number == SYS_landlock_restrict_self) {
+		pseudo_debug(PDBGF_SYSCALL, "syscall, refusing landlock.\n");
+		errno = ENOSYS;
+		return -1;
+	}
+#endif
+
 #ifdef SYS_openat2
 	/* There is a CVE patch (CVE-2025-45582) to tar 1.34 in Centos Stream which
 	 * uses syscall to access openat2() and breaks builds if we don't redirect.