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0 pointsmasklinn11d ago0 comments

> For example, Unix's `rename` syscall takes two paths as arguments; you can't rename a file by handle

And then there’s renameat(2) which takes two dirfd… and two paths from there, which mostly has all the same issues rename(2) does (and does not even take flags so even O_NOFOLLOW is not available).

I’m not sure what you’d need to make a safe renameat(), maybe a triplet of (dirfd, filefd, name[1]) from the source, (dirfd, name) from the target, and some sort of flag to indicate whether it is allowed to create, overwrite, or both.

As the recent https://blog.sebastianwick.net/posts/how-hard-is-it-to-open-... talks about (just for file but it applies to everything) secure file system interaction is absolutely heinous.

[1]: not path

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mort9611d ago

How about fd of the file you wanna rename, dirfd of the directory you want to open it in, and name of the new file? You could then represent a "rename within the same directory" as: dfd = opendir(...); fd = openat(dfd, "a"); rename2(fd, dfd, "b");

I can't think of a case this API doesn't cover, but maybe there is one.

masklinnOP11d ago

The file may have been renamed or deleted since the fd was opened, and it might have been legitimate and on purpose, but there’s no way to tell what trying to resolve the fd back to a path will give you.

And you need to do that because nothing precludes having multiple entries to the same inode in the same directory, so you need to know specifically what the source direntry is, and a direntry is just a name in the directory file.

j / k navigate · click thread line to collapse

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mort9611d ago

I can't think of a case this API doesn't cover, but maybe there is one.

masklinnOP11d ago

j / k navigate · click thread line to collapse