vfs: define struct filename and have getname() return it

getname() is intended to copy pathname strings from userspace into a
kernel buffer. The result is just a string in kernel space. It would
however be quite helpful to be able to attach some ancillary info to
the string.

For instance, we could attach some audit-related info to reduce the
amount of audit-related processing needed. When auditing is enabled,
we could also call getname() on the string more than once and not
need to recopy it from userspace.

This patchset converts the getname()/putname() interfaces to return
a struct instead of a string. For now, the struct just tracks the
string in kernel space and the original userland pointer for it.

Later, we'll add other information to the struct as it becomes
convenient.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 67 insertions, 41 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 9cc0fce7fc91..ec638d27642f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -117,18 +117,37 @@
  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
  * PATH_MAX includes the nul terminator --RR.
  */
-static char *getname_flags(const char __user *filename, int flags, int *empty)
+void final_putname(struct filename *name)
 {
-	char *result = __getname(), *err;
+	__putname(name->name);
+	kfree(name);
+}
+
+static struct filename *
+getname_flags(const char __user *filename, int flags, int *empty)
+{
+	struct filename *result, *err;
+	char *kname;
 	int len;
 
+	/* FIXME: create dedicated slabcache? */
+	result = kzalloc(sizeof(*result), GFP_KERNEL);
 	if (unlikely(!result))
 		return ERR_PTR(-ENOMEM);
 
-	len = strncpy_from_user(result, filename, PATH_MAX);
-	err = ERR_PTR(len);
-	if (unlikely(len < 0))
+	kname = __getname();
+	if (unlikely(!kname)) {
+		err = ERR_PTR(-ENOMEM);
+		goto error_free_name;
+	}
+
+	result->name = kname;
+	result->uptr = filename;
+	len = strncpy_from_user(kname, filename, PATH_MAX);
+	if (unlikely(len < 0)) {
+		err = ERR_PTR(len);
 		goto error;
+	}
 
 	/* The empty path is special. */
 	if (unlikely(!len)) {
@@ -146,22 +165,25 @@ static char *getname_flags(const char __user *filename, int flags, int *empty)
 	}
 
 error:
-	__putname(result);
+	__putname(kname);
+error_free_name:
+	kfree(result);
 	return err;
 }
 
-char *getname(const char __user * filename)
+struct filename *
+getname(const char __user * filename)
 {
 	return getname_flags(filename, 0, NULL);
 }
+EXPORT_SYMBOL(getname);
 
 #ifdef CONFIG_AUDITSYSCALL
-void putname(const char *name)
+void putname(struct filename *name)
 {
 	if (unlikely(!audit_dummy_context()))
-		audit_putname(name);
-	else
-		__putname(name);
+		return audit_putname(name);
+	final_putname(name);
 }
 #endif
 
@@ -2093,13 +2115,13 @@ int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 		 struct path *path, int *empty)
 {
 	struct nameidata nd;
-	char *tmp = getname_flags(name, flags, empty);
+	struct filename *tmp = getname_flags(name, flags, empty);
 	int err = PTR_ERR(tmp);
 	if (!IS_ERR(tmp)) {
 
 		BUG_ON(flags & LOOKUP_PARENT);
 
-		err = do_path_lookup(dfd, tmp, flags, &nd);
+		err = do_path_lookup(dfd, tmp->name, flags, &nd);
 		putname(tmp);
 		if (!err)
 			*path = nd.path;
@@ -2113,22 +2135,22 @@ int user_path_at(int dfd, const char __user *name, unsigned flags,
 	return user_path_at_empty(dfd, name, flags, path, NULL);
 }
 
-static int user_path_parent(int dfd, const char __user *path,
-			struct nameidata *nd, char **name)
+static struct filename *
+user_path_parent(int dfd, const char __user *path, struct nameidata *nd)
 {
-	char *s = getname(path);
+	struct filename *s = getname(path);
 	int error;
 
 	if (IS_ERR(s))
-		return PTR_ERR(s);
+		return s;
 
-	error = do_path_lookup(dfd, s, LOOKUP_PARENT, nd);
-	if (error)
+	error = do_path_lookup(dfd, s->name, LOOKUP_PARENT, nd);
+	if (error) {
 		putname(s);
-	else
-		*name = s;
+		return ERR_PTR(error);
+	}
 
-	return error;
+	return s;
 }
 
 /*
@@ -3039,11 +3061,11 @@ EXPORT_SYMBOL(done_path_create);
 
 struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, int is_dir)
 {
-	char *tmp = getname(pathname);
+	struct filename *tmp = getname(pathname);
 	struct dentry *res;
 	if (IS_ERR(tmp))
 		return ERR_CAST(tmp);
-	res = kern_path_create(dfd, tmp, path, is_dir);
+	res = kern_path_create(dfd, tmp->name, path, is_dir);
 	putname(tmp);
 	return res;
 }
@@ -3248,13 +3270,13 @@ out:
 static long do_rmdir(int dfd, const char __user *pathname)
 {
 	int error = 0;
-	char * name;
+	struct filename *name;
 	struct dentry *dentry;
 	struct nameidata nd;
 
-	error = user_path_parent(dfd, pathname, &nd, &name);
-	if (error)
-		return error;
+	name = user_path_parent(dfd, pathname, &nd);
+	if (IS_ERR(name))
+		return PTR_ERR(name);
 
 	switch(nd.last_type) {
 	case LAST_DOTDOT:
@@ -3343,14 +3365,14 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry)
 static long do_unlinkat(int dfd, const char __user *pathname)
 {
 	int error;
-	char *name;
+	struct filename *name;
 	struct dentry *dentry;
 	struct nameidata nd;
 	struct inode *inode = NULL;
 
-	error = user_path_parent(dfd, pathname, &nd, &name);
-	if (error)
-		return error;
+	name = user_path_parent(dfd, pathname, &nd);
+	if (IS_ERR(name))
+		return PTR_ERR(name);
 
 	error = -EISDIR;
 	if (nd.last_type != LAST_NORM)
@@ -3434,7 +3456,7 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
 		int, newdfd, const char __user *, newname)
 {
 	int error;
-	char *from;
+	struct filename *from;
 	struct dentry *dentry;
 	struct path path;
 
@@ -3447,9 +3469,9 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
 	if (IS_ERR(dentry))
 		goto out_putname;
 
-	error = security_path_symlink(&path, dentry, from);
+	error = security_path_symlink(&path, dentry, from->name);
 	if (!error)
-		error = vfs_symlink(path.dentry->d_inode, dentry, from);
+		error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
 	done_path_create(&path, dentry);
 out_putname:
 	putname(from);
@@ -3729,17 +3751,21 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
 	struct dentry *old_dentry, *new_dentry;
 	struct dentry *trap;
 	struct nameidata oldnd, newnd;
-	char *from;
-	char *to;
+	struct filename *from;
+	struct filename *to;
 	int error;
 
-	error = user_path_parent(olddfd, oldname, &oldnd, &from);
-	if (error)
+	from = user_path_parent(olddfd, oldname, &oldnd);
+	if (IS_ERR(from)) {
+		error = PTR_ERR(from);
 		goto exit;
+	}
 
-	error = user_path_parent(newdfd, newname, &newnd, &to);
-	if (error)
+	to = user_path_parent(newdfd, newname, &newnd);
+	if (IS_ERR(to)) {
+		error = PTR_ERR(to);
 		goto exit1;
+	}
 
 	error = -EXDEV;
 	if (oldnd.path.mnt != newnd.path.mnt)