Support SafeJoinPath and SafeJoinFilepath

[wolfogre]

Follow #23371.

Introduce SafeJoinPath to replace CleanPath.

CleanPath could be misused as CleanPath(path.Join("/tmp", "../etc/passwd")), and the result will be "/etc/passwd", when the right way is path.Join("/tmp", CleanPath("../etc/passwd")).

However, it will be annoying if there are many paths like path.Join("/tmp", CleanPath(input1), CleanPath(input2), CleanPath(input3)). So SafeJoinPath could do it more simply: SafeJoinPath("/tmp", input1, input2, input3).

If we really want something like CleanPath, we can just use SafeJoinPath: CleanPath(p) == SafeJoinPath(p).

Also introduce SafeJoinFilepath for filepath.Join

[wxiaoguang]

For windows: C:\foo => :\foo ?

I do not think Gitea has Windows servers to run tests .... so the test code for Windows never runs?

[wolfogre]

My bad, I thought the CI would run tests on Windows ...

I will fix it and run the tests on Windows to ensure it works.

[zeripath]

I don't think this is as helpful as you think it will be or as safe as you think it will be.

a) Do we really have that many places where we join multiple user provided paths?
b) This doesn't prevent an initial "/". So you still always have to join the path with a base path.
c) There are times when user provided ".." are appropriate or joining ".." from within code is appropriate. This will likely prevent that.

Given that #23371 is IMO unsafe I think this needs more thought.

[wxiaoguang]

I don't think this is as helpful as you think it will be or as safe as you think it will be ....

Although #23371 doesn't look good, I think we need some util functions for paths.

• There was incorrect fs.Open(path.Clean(file)) , luckily it doesn't cause security problems.
• Since action is merged, Gitea needs to operate filesystems/stroages more and more, there are already many path-related security problems during review.

So, IMO:

• We need to clearly define every path usage, absolute or relative.
• Introduce some stable and clear path util functions.

[wolfogre]

Relaced by #23495