René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[WASI] getpath.py does not handle \"Capabilities insufficient\" (ENOTCAPABLE)","articleBody":"# Bug report\r\n\r\nWASI has a capability-based security concept. A process must have a valid handle to open a resource. For example WASI runtimes let processes only open files that are inside a directory tree for which the process owns a file descriptor. wasmtime implements this with [openat2(2)](https://man7.org/linux/man-pages/man2/openat2.2.html) with flags `RESOLVE_NO_MAGICLINKS | RESOLVE_BENEATH`. Any attempt to open a file outside results in `OSError: [Errno 76] Capabilities insufficient` (`ENOTCAPABLE` / `__WASI_ERRNO_NOTCAPABLE`).\r\n\r\n`getpath.py` runs into the capability issue in several places when the module attempts to read from landmark files `VENV_LANDMARK` and `BUILDDIR_TXT`. On wasmtime the WASI process starts with CWD=`/` (root). By default the process does not have capability to access `/`. Our tests currently work around the problem by mapping on the host `SRCDIR` to `/` inside the WASI environment. Without the mapping, Python startup fails with\r\n\r\n```\r\nException ignored error evaluating path:\r\nTraceback (most recent call last):\r\n  File \"\u003cfrozen getpath\u003e\", line 353, in \u003cmodule\u003e\r\nOSError: [Errno 76] Capabilities insufficient\r\nFatal Python error: error evaluating path\r\nPython runtime state: core initialized\r\n```\r\n\r\n# Your environment\r\n\r\n`wasm32-wasi`\r\n\r\n# Fix proposal\r\n\r\n- expose `ENOTCAPABLE` in `errno` module\r\n- map `ENOTCAPABLE` to `PermissionError`. Insufficient capabilities is a sort of permission problem.\r\n- catch `PermissionError` additionally to `FileNotFoundError` at places that read `VENV_LANDMARK` and `BUILDDIR_TXT`","author":{"url":"https://github.com/tiran","@type":"Person","name":"tiran"},"datePublished":"2022-08-15T18:58:47.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/96005/cpython/issues/96005"}