NFS: support the kernel keyring for TLS

Allow tlshd to use a per-mount key from the kernel keyring similar
to NVMe over TCP.

Note that tlshd expects keys and certificates stored in the kernel
keyring to be in DER format, not the PEM format used for file based keys
and certificates, so they need to be converted before they are added
to the keyring, which is a bit unexpected.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Link: https://lore.kernel.org/r/20250515115107.33052-2-hch@lst.de
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 13f71ca8c974..9e94d18448ff 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -96,6 +96,8 @@ enum nfs_param {
 	Opt_wsize,
 	Opt_write,
 	Opt_xprtsec,
+	Opt_cert_serial,
+	Opt_privkey_serial,
 };
 
 enum {
@@ -221,6 +223,8 @@ static const struct fs_parameter_spec nfs_fs_parameters[] = {
 	fsparam_enum  ("write",		Opt_write, nfs_param_enums_write),
 	fsparam_u32   ("wsize",		Opt_wsize),
 	fsparam_string("xprtsec",	Opt_xprtsec),
+	fsparam_s32("cert_serial",	Opt_cert_serial),
+	fsparam_s32("privkey_serial",	Opt_privkey_serial),
 	{}
 };
 
@@ -551,6 +555,32 @@ static int nfs_parse_version_string(struct fs_context *fc,
 	return 0;
 }
 
+#ifdef CONFIG_KEYS
+static int nfs_tls_key_verify(key_serial_t key_id)
+{
+	struct key *key = key_lookup(key_id);
+	int error = 0;
+
+	if (IS_ERR(key)) {
+		pr_err("key id %08x not found\n", key_id);
+		return PTR_ERR(key);
+	}
+	if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
+	    test_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
+		pr_err("key id %08x revoked\n", key_id);
+		error = -EKEYREVOKED;
+	}
+
+	key_put(key);
+	return error;
+}
+#else
+static inline int nfs_tls_key_verify(key_serial_t key_id)
+{
+	return -ENOENT;
+}
+#endif /* CONFIG_KEYS */
+
 /*
  * Parse a single mount parameter.
  */
@@ -807,6 +837,18 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
 		if (ret < 0)
 			return ret;
 		break;
+	case Opt_cert_serial:
+		ret = nfs_tls_key_verify(result.int_32);
+		if (ret < 0)
+			return ret;
+		ctx->xprtsec.cert_serial = result.int_32;
+		break;
+	case Opt_privkey_serial:
+		ret = nfs_tls_key_verify(result.int_32);
+		if (ret < 0)
+			return ret;
+		ctx->xprtsec.privkey_serial = result.int_32;
+		break;
 
 	case Opt_proto:
 		if (!param->string)