|
Add a landlock_restrict_self(2) flag to set the no_new_privs attribute
of the calling thread only after enforcement of the ruleset:
no_new_privs is set if and only if the call succeeds. This removes the
need for a prior prctl(2) PR_SET_NO_NEW_PRIVS call and guarantees that
a failed enforcement leaves the attribute unchanged.
Because no_new_privs is set by the call itself, the no_new_privs /
CAP_SYS_ADMIN requirement of landlock_restrict_self(2) is fulfilled by
construction, and the related EPERM check is skipped.
Unlike LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF, this flag always
requires a valid ruleset: with a ruleset_fd of -1, such a call would be
nothing more than a Landlock-flavored prctl(2) PR_SET_NO_NEW_PRIVS, and
there is no valid use case for setting no_new_privs (possibly with
LANDLOCK_RESTRICT_SELF_TSYNC) without also enforcing Landlock
restrictions. Rejecting these calls also keeps the option of giving
them a meaning later.
The attribute is only set past the last point of failure, just before
committing the new credentials. When combined with
LANDLOCK_RESTRICT_SELF_TSYNC, no_new_privs is set on the sibling threads
as well, in their commit phase, with the same ordering.
Bump the Landlock ABI version to 11, and include the minimal related
test changes to keep the tests bisectable.
Cc: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Justin Suess <utilityemal77@gmail.com>
Link: https://patch.msgid.link/20260809212459.2427878-1-utilityemal77@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
|
|
Introduce the LANDLOCK_RESTRICT_SELF_TSYNC flag. With this flag, a
given Landlock ruleset is applied to all threads of the calling
process, instead of only the current one.
Without this flag, multithreaded userspace programs currently resort
to using the nptl(7)/libpsx hack for multithreaded policy enforcement,
which is also used by libcap and for setuid(2). Using this
userspace-based scheme, the threads of a process enforce the same
Landlock policy, but the resulting Landlock domains are still
separate. The domains being separate causes multiple problems:
* When using Landlock's "scoped" access rights, the domain identity is
used to determine whether an operation is permitted. As a result,
when using LANLDOCK_SCOPE_SIGNAL, signaling between sibling threads
stops working. This is a problem for programming languages and
frameworks which are inherently multithreaded (e.g. Go).
* In audit logging, the domains of separate threads in a process will
get logged with different domain IDs, even when they are based on
the same ruleset FD, which might confuse users.
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Paul Moore <paul@paul-moore.com>
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20251127115136.3064948-2-gnoack@google.com
[mic: Fix restrict_self_flags test, clean up Makefile, allign comments,
reduce local variable scope, add missing includes]
Closes: https://github.com/landlock-lsm/linux/issues/2
Signed-off-by: Mickaël Salaün <mic@digikod.net>
|
