Re: [RFC PATCH] f*xattr: allow O_PATH descriptors

On Wed, Jun 8, 2022 at 9:01 PM Andreas Dilger [off-list ref] wrote:

On Jun 7, 2022, at 9:31 AM, Christian Göttsche [off-list ref] wrote:

quoted

From: Miklos Szeredi <redacted>

Support file descriptors obtained via O_PATH for extended attribute
operations.

Extended attributes are for example used by SELinux for the security
context of file objects. To avoid time-of-check-time-of-use issues while
setting those contexts it is advisable to pin the file in question and
operate on a file descriptor instead of the path name. This can be
emulated in userspace via /proc/self/fd/NN [1] but requires a procfs,
which might not be mounted e.g. inside of chroots, see[2].

Will this allow get/set xattrs directly on symlinks?  That is one problem
that we have with some of the xattrs that are inherited on symlinks, but
there is no way to change them.  Allowing setxattr directly on a symlink
would be very useful.

It is possible.
See: https://github.com/libfuse/libfuse/pull/514

That's why Miklos withdrew this patch:
https://lore.kernel.org/linux-fsdevel/CAOssrKeV7g0wPg4ozspG4R7a+5qARqWdG+GxWtXB-MCfbVM=9A@mail.gmail.com/ (local)

Thanks,
Amir.