gh-145335: Fix crash when passing -1 as fd in os.pathconf

[aisk]

We currently test whether path_t.fd is -1 to decide if the argument should be treated as an fd or as a path, and then call fpathconf() or pathconf() according to it.

In the original issue, we passing -1 caused the code incorrectly treats the argument as a real path. But, path->narrow is NULL, so calling pathconf() on it will crash the interpreter.

This change adds a helper that checks whether the original argument is index-like to determine if it's an fd, so we can correctly the behavior and avoid the crash.

There are other os functions that accept path_t and may have the same issue. Since that is outside the scope of the original issue, I think we should fix those in a separate PR.

• Issue: Segfault from running os.pathconf(-1, 1) #145335

[picnixz]

Is the problem really with the check or with is it with the converter?

[picnixz]

edit: nvm

[vstinner]

Instead of checking path->object type (PyIndex_Check()), I would prefer adding a path_t.is_fd member and modify path_converter() to set this member.

[aisk]

Updated.

[vstinner]

Other functions have the same issues, even if they don't crash:

• os.stat(-1)
• os.statx(-1, mask=0)
• os.chdir(-1)
• os.chmod(-1, 0)
• os.chown(-1, 0, 0)
• os.listdir(-1): current it behaves as os.listdir(os.path.curdir)
• os._path_exists(-1) (Windows only)
• os._path_lexists(-1) (Windows only)
• os._path_isdir(-1) (Windows only)
• os._path_isfile(-1) (Windows only)
• os._path_islink(-1) (Windows only)
• os._path_isjunction(-1) (Windows only)
• os.utime(-1, (0, 0))
• os.execve(-1, ['/bin/true'], os.environ)
• os.truncate(-1, 0)
• os.statvfs(-1)
• os.pathconf(-1, "PC_NAME_MAX") crash (issue Segfault from running os.pathconf(-1, 1) #145335)
• os.getxattr(-1, "user")
• os.setxattr(-1, "user", b"1")
• os.removexattr(-1, "user")
• os.listxattr(-1): current it behaves as os.listxattr(os.path.curdir)
• os.scandir(-1): current it behaves as os.scandir(os.path.curdir)

On Linux (with the glibc), most functions fail with OSError: [Errno 14] Bad address: -1.

This list are functions using path_t(allow_fd=True) type in Argument Clinic, or variants such as path_t(allow_fd='PATH_HAVE_FCHDIR') type.