Commit 7303515a authored Jul 03, 2020 by Kees Cook Committed by Jonathan Corbet Jul 05, 2020

Documentation: Clarify f_cred vs current_cred() use

When making access control choices from a file-based context, f_cred
must be used instead of current_cred() to avoid confused deputy attacks
where an open file may get passed to a more privileged process. Add a
short paragraph to explicitly state the rationale.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/202007031038.8833A35DE4@keescook

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

parent 559394d3

Documentation/security/credentials.rst

+4 −0

Original line number	Diff line number	Diff line
		@@ -548,6 +548,10 @@ pointer will not change over the lifetime of the file struct, and nor will the
		contents of the cred struct pointed to, barring the exceptions listed above
		(see the Task Credentials section).

		To avoid "confused deputy" privilege escalation attacks, access control checks
		during subsequent operations on an opened file should use these credentials
		instead of "current"'s credentials, as the file may have been passed to a more
		privileged process.

		Overriding the VFS's Use of Credentials
		=======================================

Admin message