fscrypt updates for 5.7

Add an ioctl FS_IOC_GET_ENCRYPTION_NONCE which retrieves a file's
 encryption nonce.  This makes it easier to write automated tests which
 verify that fscrypt is doing the encryption correctly.
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Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt

Pull fscrypt updates from Eric Biggers:
 "Add an ioctl FS_IOC_GET_ENCRYPTION_NONCE which retrieves a file's
  encryption nonce.

  This makes it easier to write automated tests which verify that
  fscrypt is doing the encryption correctly"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
  ubifs: wire up FS_IOC_GET_ENCRYPTION_NONCE
  f2fs: wire up FS_IOC_GET_ENCRYPTION_NONCE
  ext4: wire up FS_IOC_GET_ENCRYPTION_NONCE
  fscrypt: add FS_IOC_GET_ENCRYPTION_NONCE ioctl

Documentation/filesystems/fscrypt.rst

@@ -633,6 +633,17 @@ from a passphrase or other low-entropy user credential.
 FS_IOC_GET_ENCRYPTION_PWSALT is deprecated.  Instead, prefer to
 generate and manage any needed salt(s) in userspace.
 
+Getting a file's encryption nonce
+---------------------------------
+
+Since Linux v5.7, the ioctl FS_IOC_GET_ENCRYPTION_NONCE is supported.
+On encrypted files and directories it gets the inode's 16-byte nonce.
+On unencrypted files and directories, it fails with ENODATA.
+
+This ioctl can be useful for automated tests which verify that the
+encryption is being done correctly.  It is not needed for normal use
+of fscrypt.
+
 Adding keys
 -----------
 

fs/crypto/fscrypt_private.h

@@ -76,6 +76,26 @@ static inline int fscrypt_context_size(const union fscrypt_context *ctx)
 	return 0;
 }
 
+/* Check whether an fscrypt_context has a recognized version number and size */
+static inline bool fscrypt_context_is_valid(const union fscrypt_context *ctx,
+					    int ctx_size)
+{
+	return ctx_size >= 1 && ctx_size == fscrypt_context_size(ctx);
+}
+
+/* Retrieve the context's nonce, assuming the context was already validated */
+static inline const u8 *fscrypt_context_nonce(const union fscrypt_context *ctx)
+{
+	switch (ctx->version) {
+	case FSCRYPT_CONTEXT_V1:
+		return ctx->v1.nonce;
+	case FSCRYPT_CONTEXT_V2:
+		return ctx->v2.nonce;
+	}
+	WARN_ON(1);
+	return NULL;
+}
+
 #undef fscrypt_policy
 union fscrypt_policy {
 	u8 version;

fs/crypto/keysetup.c

@@ -425,20 +425,8 @@ int fscrypt_get_encryption_info(struct inode *inode)
 		goto out;
 	}
 
-	switch (ctx.version) {
-	case FSCRYPT_CONTEXT_V1:
-		memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
-		       FS_KEY_DERIVATION_NONCE_SIZE);
-		break;
-	case FSCRYPT_CONTEXT_V2:
-		memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
-		       FS_KEY_DERIVATION_NONCE_SIZE);
-		break;
-	default:
-		WARN_ON(1);
-		res = -EINVAL;
-		goto out;
-	}
+	memcpy(crypt_info->ci_nonce, fscrypt_context_nonce(&ctx),
+	       FS_KEY_DERIVATION_NONCE_SIZE);
 
 	if (!fscrypt_supported_policy(&crypt_info->ci_policy, inode)) {
 		res = -EINVAL;

fs/crypto/policy.c

@@ -258,7 +258,7 @@ int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
 {
 	memset(policy_u, 0, sizeof(*policy_u));
 
-	if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
+	if (!fscrypt_context_is_valid(ctx_u, ctx_size))
 		return -EINVAL;
 
 	switch (ctx_u->version) {
@@ -481,6 +481,25 @@ int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);
 
+/* FS_IOC_GET_ENCRYPTION_NONCE: retrieve file's encryption nonce for testing */
+int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg)
+{
+	struct inode *inode = file_inode(filp);
+	union fscrypt_context ctx;
+	int ret;
+
+	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
+	if (ret < 0)
+		return ret;
+	if (!fscrypt_context_is_valid(&ctx, ret))
+		return -EINVAL;
+	if (copy_to_user(arg, fscrypt_context_nonce(&ctx),
+			 FS_KEY_DERIVATION_NONCE_SIZE))
+		return -EFAULT;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_nonce);
+
 /**
  * fscrypt_has_permitted_context() - is a file's encryption policy permitted
  *				     within its directory?

fs/ext4/ioctl.c

@@ -1210,6 +1210,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			return -EOPNOTSUPP;
 		return fscrypt_ioctl_get_key_status(filp, (void __user *)arg);
 
+	case FS_IOC_GET_ENCRYPTION_NONCE:
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+		return fscrypt_ioctl_get_nonce(filp, (void __user *)arg);
+
 	case EXT4_IOC_CLEAR_ES_CACHE:
 	{
 		if (!inode_owner_or_capable(inode))
@@ -1370,6 +1375,7 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FS_IOC_REMOVE_ENCRYPTION_KEY:
 	case FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS:
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+	case FS_IOC_GET_ENCRYPTION_NONCE:
 	case EXT4_IOC_SHUTDOWN:
 	case FS_IOC_GETFSMAP:
 	case FS_IOC_ENABLE_VERITY:

fs/f2fs/file.c

@@ -2423,6 +2423,14 @@ static int f2fs_ioc_get_encryption_key_status(struct file *filp,
 	return fscrypt_ioctl_get_key_status(filp, (void __user *)arg);
 }
 
+static int f2fs_ioc_get_encryption_nonce(struct file *filp, unsigned long arg)
+{
+	if (!f2fs_sb_has_encrypt(F2FS_I_SB(file_inode(filp))))
+		return -EOPNOTSUPP;
+
+	return fscrypt_ioctl_get_nonce(filp, (void __user *)arg);
+}
+
 static int f2fs_ioc_gc(struct file *filp, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -3437,6 +3445,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_remove_encryption_key_all_users(filp, arg);
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
 		return f2fs_ioc_get_encryption_key_status(filp, arg);
+	case FS_IOC_GET_ENCRYPTION_NONCE:
+		return f2fs_ioc_get_encryption_nonce(filp, arg);
 	case F2FS_IOC_GARBAGE_COLLECT:
 		return f2fs_ioc_gc(filp, arg);
 	case F2FS_IOC_GARBAGE_COLLECT_RANGE:
@@ -3611,6 +3621,7 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FS_IOC_REMOVE_ENCRYPTION_KEY:
 	case FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS:
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+	case FS_IOC_GET_ENCRYPTION_NONCE:
 	case F2FS_IOC_GARBAGE_COLLECT:
 	case F2FS_IOC_GARBAGE_COLLECT_RANGE:
 	case F2FS_IOC_WRITE_CHECKPOINT:

fs/ubifs/ioctl.c

@@ -208,6 +208,9 @@ long ubifs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
 		return fscrypt_ioctl_get_key_status(file, (void __user *)arg);
 
+	case FS_IOC_GET_ENCRYPTION_NONCE:
+		return fscrypt_ioctl_get_nonce(file, (void __user *)arg);
+
 	default:
 		return -ENOTTY;
 	}
@@ -230,6 +233,7 @@ long ubifs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FS_IOC_REMOVE_ENCRYPTION_KEY:
 	case FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS:
 	case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
+	case FS_IOC_GET_ENCRYPTION_NONCE:
 		break;
 	default:
 		return -ENOIOCTLCMD;

include/linux/fscrypt.h

@@ -139,6 +139,7 @@ extern void fscrypt_free_bounce_page(struct page *bounce_page);
 extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
 extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
 extern int fscrypt_ioctl_get_policy_ex(struct file *, void __user *);
+extern int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg);
 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
 extern int fscrypt_inherit_context(struct inode *, struct inode *,
 					void *, bool);
@@ -300,6 +301,11 @@ static inline int fscrypt_ioctl_get_policy_ex(struct file *filp,
 	return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int fscrypt_has_permitted_context(struct inode *parent,
 						struct inode *child)
 {

include/uapi/linux/fscrypt.h

@@ -163,6 +163,7 @@ struct fscrypt_get_key_status_arg {
 #define FS_IOC_REMOVE_ENCRYPTION_KEY		_IOWR('f', 24, struct fscrypt_remove_key_arg)
 #define FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS	_IOWR('f', 25, struct fscrypt_remove_key_arg)
 #define FS_IOC_GET_ENCRYPTION_KEY_STATUS	_IOWR('f', 26, struct fscrypt_get_key_status_arg)
+#define FS_IOC_GET_ENCRYPTION_NONCE		_IOR('f', 27, __u8[16])
 
 /**********************************************************************/