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INVALID_VFS{U,G}ID represent ids which have no mapping in the target
mnt_usersns. This can happen for a couple of different reasons -- the
source id might be valid but has no mapping in mnt_userns, or the source
id might have been invalid (either due to a failed mapping or because it
was set to invalid to indicate it is uninitialized).
This means that two arbitrary vfs{u,g}ids which are both invalid could
represent two different underlying ids, or they could represent a failed
mapping and an uninitialized value. In these situation the vfs{u,g}id
equality functions evaluate these ids as equal, and care must be taken
when comparing ids to avoid problems. It would be less error prone to
always evaluate two invalid ids as not equal to each other, and to check
explicitly for vfs{u,g}id validity when that is needed.
Change all vfs{u,g}id equality functions to return false when both ids
are invalid. Functions for checking whether an id is valid exist and are
already being used by code which needs to check this.
Link: https://lore.kernel.org/linux-fsdevel/YrIMZirGoE0VIO45@do-x1extreme
Signed-off-by: Seth Forshee <sforshee@digitalocean.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.