introduce cloning of fs_context

new primitive: vfs_dup_fs_context().  Comes with fs_context
method (->dup()) for copying the filesystem-specific parts
of fs_context, along with LSM one (->fs_context_dup()) for
doing the same to LSM parts.

[needs better commit message, and change of Author:, anyway]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/fs_context.c

@@ -337,6 +337,47 @@ void fc_drop_locked(struct fs_context *fc)
 
 static void legacy_fs_context_free(struct fs_context *fc);
 
+/**
+ * vfs_dup_fc_config: Duplicate a filesystem context.
+ * @src_fc: The context to copy.
+ */
+struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
+{
+	struct fs_context *fc;
+	int ret;
+
+	if (!src_fc->ops->dup)
+		return ERR_PTR(-EOPNOTSUPP);
+
+	fc = kmemdup(src_fc, sizeof(struct fs_context), GFP_KERNEL);
+	if (!fc)
+		return ERR_PTR(-ENOMEM);
+
+	fc->fs_private	= NULL;
+	fc->s_fs_info	= NULL;
+	fc->source	= NULL;
+	fc->security	= NULL;
+	get_filesystem(fc->fs_type);
+	get_net(fc->net_ns);
+	get_user_ns(fc->user_ns);
+	get_cred(fc->cred);
+
+	/* Can't call put until we've called ->dup */
+	ret = fc->ops->dup(fc, src_fc);
+	if (ret < 0)
+		goto err_fc;
+
+	ret = security_fs_context_dup(fc, src_fc);
+	if (ret < 0)
+		goto err_fc;
+	return fc;
+
+err_fc:
+	put_fs_context(fc);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(vfs_dup_fs_context);
+
 /**
  * put_fs_context - Dispose of a superblock configuration context.
  * @fc: The context to dispose of.
@@ -380,6 +421,31 @@ static void legacy_fs_context_free(struct fs_context *fc)
 	}
 }
 
+/*
+ * Duplicate a legacy config.
+ */
+static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
+{
+	struct legacy_fs_context *ctx;
+	struct legacy_fs_context *src_ctx = src_fc->fs_private;
+
+	ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	if (ctx->param_type == LEGACY_FS_INDIVIDUAL_PARAMS) {
+		ctx->legacy_data = kmemdup(src_ctx->legacy_data,
+					   src_ctx->data_size, GFP_KERNEL);
+		if (!ctx->legacy_data) {
+			kfree(ctx);
+			return -ENOMEM;
+		}
+	}
+
+	fc->fs_private = ctx;
+	return 0;
+}
+
 /*
  * Add a parameter to a legacy config.  We build up a comma-separated list of
  * options.
@@ -514,6 +580,7 @@ static int legacy_reconfigure(struct fs_context *fc)
 
 const struct fs_context_operations legacy_fs_context_ops = {
 	.free			= legacy_fs_context_free,
+	.dup			= legacy_fs_context_dup,
 	.parse_param		= legacy_parse_param,
 	.parse_monolithic	= legacy_parse_monolithic,
 	.get_tree		= legacy_get_tree,

include/linux/fs_context.h

@@ -94,6 +94,7 @@ struct fs_context {
 
 struct fs_context_operations {
 	void (*free)(struct fs_context *fc);
+	int (*dup)(struct fs_context *fc, struct fs_context *src_fc);
 	int (*parse_param)(struct fs_context *fc, struct fs_parameter *param);
 	int (*parse_monolithic)(struct fs_context *fc, void *data);
 	int (*get_tree)(struct fs_context *fc);
@@ -111,6 +112,7 @@ extern struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
 extern struct fs_context *fs_context_for_submount(struct file_system_type *fs_type,
 						struct dentry *reference);
 
+extern struct fs_context *vfs_dup_fs_context(struct fs_context *fc);
 extern int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param);
 extern int vfs_parse_fs_string(struct fs_context *fc, const char *key,
 			       const char *value, size_t v_size);

include/linux/lsm_hooks.h

@@ -79,6 +79,11 @@
  * Security hooks for mount using fs_context.
  *	[See also Documentation/filesystems/mounting.txt]
  *
+ * @fs_context_dup:
+ *	Allocate and attach a security structure to sc->security.  This pointer
+ *	is initialised to NULL by the caller.
+ *	@fc indicates the new filesystem context.
+ *	@src_fc indicates the original filesystem context.
  * @fs_context_parse_param:
  *	Userspace provided a parameter to configure a superblock.  The LSM may
  *	reject it with an error and may use it for itself, in which case it
@@ -1470,6 +1475,7 @@ union security_list_options {
 	void (*bprm_committing_creds)(struct linux_binprm *bprm);
 	void (*bprm_committed_creds)(struct linux_binprm *bprm);
 
+	int (*fs_context_dup)(struct fs_context *fc, struct fs_context *src_sc);
 	int (*fs_context_parse_param)(struct fs_context *fc, struct fs_parameter *param);
 
 	int (*sb_alloc_security)(struct super_block *sb);
@@ -1813,6 +1819,7 @@ struct security_hook_heads {
 	struct hlist_head bprm_check_security;
 	struct hlist_head bprm_committing_creds;
 	struct hlist_head bprm_committed_creds;
+	struct hlist_head fs_context_dup;
 	struct hlist_head fs_context_parse_param;
 	struct hlist_head sb_alloc_security;
 	struct hlist_head sb_free_security;

include/linux/security.h

@@ -223,6 +223,7 @@ int security_bprm_set_creds(struct linux_binprm *bprm);
 int security_bprm_check(struct linux_binprm *bprm);
 void security_bprm_committing_creds(struct linux_binprm *bprm);
 void security_bprm_committed_creds(struct linux_binprm *bprm);
+int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc);
 int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param);
 int security_sb_alloc(struct super_block *sb);
 void security_sb_free(struct super_block *sb);
@@ -521,6 +522,11 @@ static inline void security_bprm_committed_creds(struct linux_binprm *bprm)
 {
 }
 
+static inline int security_fs_context_dup(struct fs_context *fc,
+					  struct fs_context *src_fc)
+{
+	return 0;
+}
 static inline int security_fs_context_parse_param(struct fs_context *fc,
 						  struct fs_parameter *param)
 {

security/security.c

@@ -374,6 +374,11 @@ void security_bprm_committed_creds(struct linux_binprm *bprm)
 	call_void_hook(bprm_committed_creds, bprm);
 }
 
+int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
+{
+	return call_int_hook(fs_context_dup, 0, fc, src_fc);
+}
+
 int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	return call_int_hook(fs_context_parse_param, -ENOPARAM, fc, param);

security/selinux/hooks.c

@@ -2764,6 +2764,44 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
 				   FILESYSTEM__UNMOUNT, NULL);
 }
 
+static int selinux_fs_context_dup(struct fs_context *fc,
+				  struct fs_context *src_fc)
+{
+	const struct selinux_mnt_opts *src = src_fc->security;
+	struct selinux_mnt_opts *opts;
+
+	if (!src)
+		return 0;
+
+	fc->security = kzalloc(sizeof(struct selinux_mnt_opts), GFP_KERNEL);
+	if (!fc->security)
+		return -ENOMEM;
+
+	opts = fc->security;
+
+	if (src->fscontext) {
+		opts->fscontext = kstrdup(src->fscontext, GFP_KERNEL);
+		if (!opts->fscontext)
+			return -ENOMEM;
+	}
+	if (src->context) {
+		opts->context = kstrdup(src->context, GFP_KERNEL);
+		if (!opts->context)
+			return -ENOMEM;
+	}
+	if (src->rootcontext) {
+		opts->rootcontext = kstrdup(src->rootcontext, GFP_KERNEL);
+		if (!opts->rootcontext)
+			return -ENOMEM;
+	}
+	if (src->defcontext) {
+		opts->defcontext = kstrdup(src->defcontext, GFP_KERNEL);
+		if (!opts->defcontext)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
 static const struct fs_parameter_spec selinux_param_specs[] = {
 	fsparam_string(CONTEXT_STR,	Opt_context),
 	fsparam_string(DEFCONTEXT_STR,	Opt_defcontext),
@@ -6745,6 +6783,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds),
 	LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
 
+	LSM_HOOK_INIT(fs_context_dup, selinux_fs_context_dup),
 	LSM_HOOK_INIT(fs_context_parse_param, selinux_fs_context_parse_param),
 
 	LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),

security/smack/smack_lsm.c

@@ -647,6 +647,54 @@ static int smack_add_opt(int token, const char *s, void **mnt_opts)
 	return -EINVAL;
 }
 
+/**
+ * smack_fs_context_dup - Duplicate the security data on fs_context duplication
+ * @fc: The new filesystem context.
+ * @src_fc: The source filesystem context being duplicated.
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_dup(struct fs_context *fc,
+				struct fs_context *src_fc)
+{
+	struct smack_mnt_opts *dst, *src = src_fc->security;
+
+	if (!src)
+		return 0;
+
+	fc->security = kzalloc(sizeof(struct smack_mnt_opts), GFP_KERNEL);
+	if (!fc->security)
+		return -ENOMEM;
+	dst = fc->security;
+
+	if (src->fsdefault) {
+		dst->fsdefault = kstrdup(src->fsdefault, GFP_KERNEL);
+		if (!dst->fsdefault)
+			return -ENOMEM;
+	}
+	if (src->fsfloor) {
+		dst->fsfloor = kstrdup(src->fsfloor, GFP_KERNEL);
+		if (!dst->fsfloor)
+			return -ENOMEM;
+	}
+	if (src->fshat) {
+		dst->fshat = kstrdup(src->fshat, GFP_KERNEL);
+		if (!dst->fshat)
+			return -ENOMEM;
+	}
+	if (src->fsroot) {
+		dst->fsroot = kstrdup(src->fsroot, GFP_KERNEL);
+		if (!dst->fsroot)
+			return -ENOMEM;
+	}
+	if (src->fstransmute) {
+		dst->fstransmute = kstrdup(src->fstransmute, GFP_KERNEL);
+		if (!dst->fstransmute)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
 static const struct fs_parameter_spec smack_param_specs[] = {
 	fsparam_string("fsdefault",	Opt_fsdefault),
 	fsparam_string("fsfloor",	Opt_fsfloor),
@@ -4626,6 +4674,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_traceme, smack_ptrace_traceme),
 	LSM_HOOK_INIT(syslog, smack_syslog),
 
+	LSM_HOOK_INIT(fs_context_dup, smack_fs_context_dup),
 	LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),
 
 	LSM_HOOK_INIT(sb_alloc_security, smack_sb_alloc_security),