fix: document FIPS v5 reseed suppression and genkey privilege requirement

Author: MarkAtwood

README.md

@@ -162,6 +162,14 @@ under `/lib/modules/` where the target kernel's modules are installed.
 The `genkey` and `pubkey` ops in the final line are basic functionality tests.
 If all is well, it will succeed, and print a random public key.
 
+**Note:** When the `wolfguard.ko` kernel module is loaded, `wg genkey` (and
+`wg-fips genkey`) offloads key generation to the kernel module via netlink and
+therefore requires `CAP_NET_ADMIN`.  Non-root users will receive a permission
+error.  To resolve this, either run as root or via `sudo`, or build `wg-fips`
+with `NO_IPC_LLCRYPTO=1` (which selects the userspace key generation path), or
+grant the `wg-fips` binary the `cap_net_admin` file capability
+(`setcap cap_net_admin+ep wg-fips`).
+
 As for the `wg-fips` build above, compressed public key support can be enabled
 by adding `EXTRA_CFLAGS=-DWG_USE_PUBLIC_KEY_COMPRESSION` to the above `make`
 recipe.  The `WG_USE_PUBLIC_KEY_COMPRESSION` setting must be matched throughout
@@ -296,6 +304,14 @@ $ ../user-src/wg-fips genkey | ../user-src/wg-fips pubkey
 The `genkey` and `pubkey` ops in the final line are basic functionality tests.
 If all is well, it will succeed, and print a random public key.
 
+**Note:** When the `wolfguard.ko` kernel module is loaded, `wg genkey` (and
+`wg-fips genkey`) offloads key generation to the kernel module via netlink and
+therefore requires `CAP_NET_ADMIN`.  Non-root users will receive a permission
+error.  To resolve this, either run as root or via `sudo`, or build `wg-fips`
+with `NO_IPC_LLCRYPTO=1` (which selects the userspace key generation path), or
+grant the `wg-fips` binary the `cap_net_admin` file capability
+(`setcap cap_net_admin+ep wg-fips`).
+
 As with the non-FIPS-certified procedure, if all of the above succeeds, then you
 are now ready to bring up WolfGuard tunnels.  Existing playbooks and scripting
 for WireGuard can be used directly, provided you substitute `/etc/wolfguard` for

kernel-src/netlink.c

@@ -876,6 +876,13 @@ struct genl_ops genl_ops[] = {
 #endif
 		.flags = GENL_UNS_ADMIN_PERM
 	}, {
+		/* Key generation is offloaded to the kernel module and
+		 * therefore requires CAP_NET_ADMIN.  Users without this
+		 * privilege should either run via sudo/root, or build
+		 * with NO_IPC_LLCRYPTO=1 to use the userspace key
+		 * generation path, or ensure the wg-fips binary has the
+		 * appropriate file capabilities set (e.g. cap_net_admin+ep).
+		 */
 		.cmd = WG_CMD_GEN_PRIVKEY,
 		.doit = wg_nl_generate_privkey,
 		.policy = device_policy,

kernel-src/wolfcrypt_glue.c

@@ -1196,6 +1196,10 @@ int wc_linuxkm_drbg_generate(struct wc_linuxkm_drbg_ctx *ctx,
 retry:
 
 #if defined(HAVE_FIPS) && FIPS_VERSION_LT(6,0)
+    /* FIPS v5 does not expose an API to externally reseed the DRBG.
+     * The entropy input is therefore discarded here.  The DRBG output
+     * remains safe: it was properly seeded at initialization time.
+     */
     (void)src;
     (void)slen;
 #else