namei: make do_linkat() take struct filename

Pass in the struct filename pointers instead of the user string, for
uniformity with do_renameat2, do_unlinkat, do_mknodat, etc.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/20210330071700.kpjoyp5zlni7uejm@wittgenstein/Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20210708063447.3556403-8-dkadashev@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/namei.c

@@ -2467,7 +2467,7 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
 	return err;
 }
 
-int filename_lookup(int dfd, struct filename *name, unsigned flags,
+static int __filename_lookup(int dfd, struct filename *name, unsigned flags,
 		    struct path *path, struct path *root)
 {
 	int retval;
@@ -2485,6 +2485,14 @@ int filename_lookup(int dfd, struct filename *name, unsigned flags,
 		audit_inode(name, path->dentry,
 			    flags & LOOKUP_MOUNTPOINT ? AUDIT_INODE_NOEVAL : 0);
 	restore_nameidata();
+	return retval;
+}
+
+int filename_lookup(int dfd, struct filename *name, unsigned flags,
+		    struct path *path, struct path *root)
+{
+	int retval = __filename_lookup(dfd, name, flags, path, root);
+
 	putname(name);
 	return retval;
 }
@@ -4361,8 +4369,8 @@ EXPORT_SYMBOL(vfs_link);
  * with linux 2.0, and to avoid hard-linking to directories
  * and other special files.  --ADM
  */
-static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
-	      const char __user *newname, int flags)
+static int do_linkat(int olddfd, struct filename *old, int newdfd,
+	      struct filename *new, int flags)
 {
 	struct user_namespace *mnt_userns;
 	struct dentry *new_dentry;
@@ -4371,31 +4379,32 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 	int how = 0;
 	int error;
 
-	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
-		return -EINVAL;
+	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) {
+		error = -EINVAL;
+		goto out_putnames;
+	}
 	/*
 	 * To use null names we require CAP_DAC_READ_SEARCH
 	 * This ensures that not everyone will be able to create
 	 * handlink using the passed filedescriptor.
 	 */
-	if (flags & AT_EMPTY_PATH) {
-		if (!capable(CAP_DAC_READ_SEARCH))
-			return -ENOENT;
-		how = LOOKUP_EMPTY;
+	if (flags & AT_EMPTY_PATH && !capable(CAP_DAC_READ_SEARCH)) {
+		error = -ENOENT;
+		goto out_putnames;
 	}
 
 	if (flags & AT_SYMLINK_FOLLOW)
 		how |= LOOKUP_FOLLOW;
 retry:
-	error = user_path_at(olddfd, oldname, how, &old_path);
+	error = __filename_lookup(olddfd, old, how, &old_path, NULL);
 	if (error)
-		return error;
+		goto out_putnames;
 
-	new_dentry = user_path_create(newdfd, newname, &new_path,
+	new_dentry = __filename_create(newdfd, new, &new_path,
 					(how & LOOKUP_REVAL));
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
-		goto out;
+		goto out_putpath;
 
 	error = -EXDEV;
 	if (old_path.mnt != new_path.mnt)
@@ -4423,8 +4432,11 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 		how |= LOOKUP_REVAL;
 		goto retry;
 	}
-out:
+out_putpath:
 	path_put(&old_path);
+out_putnames:
+	putname(old);
+	putname(new);
 
 	return error;
 }
@@ -4432,12 +4444,13 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 		int, newdfd, const char __user *, newname, int, flags)
 {
-	return do_linkat(olddfd, oldname, newdfd, newname, flags);
+	return do_linkat(olddfd, getname_uflags(oldname, flags),
+		newdfd, getname(newname), flags);
 }
 
 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
 {
-	return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
+	return do_linkat(AT_FDCWD, getname(oldname), AT_FDCWD, getname(newname), 0);
 }
 
 /**