Fix security issues with filesystems, 2nd attempt (#70)

src/Zio.Tests/FileSystems/TestPhysicalFileSystem.cs

@@ -149,6 +149,10 @@ public void TestDirectorySpecial()
         public void TestDirectoryExceptions()
         {
             var fs = new PhysicalFileSystem();
+
+            // Test invalid characters in path
+            Assert.Throws<ArgumentException>(() => fs.CreateFile($"/##/mnt/hello".Replace("#", char.ConvertFromUtf32(0xad))));
+
             // Try to create a folder on an unauthorized location
             fs.CreateDirectory("/");
             Assert.Throws<UnauthorizedAccessException>(() => fs.CreateDirectory("/mnt2"));

src/Zio/FileSystems/PhysicalFileSystem.cs

@@ -800,7 +800,7 @@ protected override string ConvertPathToInternalImpl(UPath path)
 
             if (IsOnWindows)
             {
-                if (!absolutePath.StartsWith(DrivePrefixOnWindows) ||
+                if (!absolutePath.StartsWith(DrivePrefixOnWindows, StringComparison.Ordinal) ||
                     absolutePath.Length == DrivePrefixOnWindows.Length ||
                     !IsDriveLetter(absolutePath[DrivePrefixOnWindows.Length]))
                     throw new ArgumentException($"A path on Windows must start by `{DrivePrefixOnWindows}` followed by the drive letter");
@@ -829,7 +829,7 @@ protected override UPath ConvertPathFromInternalImpl(string innerPath)
             if (IsOnWindows)
             {
                 // We currently don't support special Windows files (\\.\ \??\  DosDevices...etc.)
-                if (innerPath.StartsWith(@"\\") || innerPath.StartsWith(@"\?"))
+                if (innerPath.StartsWith(@"\\", StringComparison.Ordinal) || innerPath.StartsWith(@"\?", StringComparison.Ordinal))
                     throw new NotSupportedException($"Path starting with `\\\\` or `\\?` are not supported -> `{innerPath}` ");
 
                 var absolutePath = Path.GetFullPath(innerPath);

src/Zio/FileSystems/SubFileSystem.cs

@@ -79,7 +79,7 @@ protected override UPath ConvertPathToDelegate(UPath path)
         protected override UPath ConvertPathFromDelegate(UPath path)
         {
             var fullPath = path.FullName;
-            if (!fullPath.StartsWith(SubPath.FullName) || (fullPath.Length > SubPath.FullName.Length && fullPath[SubPath.FullName.Length] != UPath.DirectorySeparator))
+            if (!fullPath.StartsWith(SubPath.FullName, StringComparison.Ordinal) || (fullPath.Length > SubPath.FullName.Length && fullPath[SubPath.FullName.Length] != UPath.DirectorySeparator))
             {
                 // More a safe guard, as it should never happen, but if a delegate filesystem doesn't respect its root path
                 // we are throwing an exception here

src/Zio/SearchPattern.cs

@@ -79,7 +79,7 @@ private SearchPattern(ref UPath path, ref string searchPattern)
                 return;
             }
 
-            if (searchPattern.StartsWith("/"))
+            if (searchPattern.StartsWith("/", StringComparison.Ordinal))
             {
                 throw new ArgumentException($"The search pattern `{searchPattern}` cannot start by an absolute path `/`");
             }

src/Zio/UPath.cs

@@ -90,7 +90,7 @@ internal UPath(string path, bool safe)
         /// Gets a value indicating whether this path is absolute by starting with a leading `/`.
         /// </summary>
         /// <value><c>true</c> if this path is absolute; otherwise, <c>false</c>.</value>
-        public bool IsAbsolute => FullName?.StartsWith("/") ?? false;
+        public bool IsAbsolute => FullName?.StartsWith("/", StringComparison.Ordinal) ?? false;
 
         /// <summary>
         /// Gets a value indicating whether this path is relative by **not** starting with a leading `/`.

src/Zio/UPathExtensions.cs

@@ -200,7 +200,7 @@ public static bool IsInDirectory(this UPath path, UPath directory, bool recursiv
             var target = path.FullName;
             var dir = directory.FullName;
 
-            if (target.Length < dir.Length || !target.StartsWith(dir))
+            if (target.Length < dir.Length || !target.StartsWith(dir, StringComparison.Ordinal))
             {
                 return false;
             }