typo: Subject's LimigtNPROC -> LimitNPROC On Thu, Feb 24, 2022 at 09:41:44AM -0600, Eric W. Biederman wrote: > > Long story short recursively enforcing RLIMIT_NPROC when it is not > enforced on the process that creates a new user namespace, causes > currently working code to fail. There is no reason to enforce > RLIMIT_NPROC recursively when we don't enforce it normally so update > the code to detect this case. > > I would like to simply use capable(CAP_SYS_RESOURCE) to detect when > RLIMIT_NPROC is not enforced upon the caller. Unfortunately because > RLIMIT_NPROC is charged and checked for enforcement based upon the > real uid, using capable() wich is euid based is inconsistent with reality. typo: wich -> which > Come as close as possible to testing for capable(CAP_SYS_RESOURCE) by > testing for when the real uid would match the conditions when > CAP_SYS_RESOURCE would be present if the real uid was the effective > uid. > > Reported-by: Etienne Dechamps <etienne@xxxxxxxxxxxx> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=215596 > Link: https://lkml.kernel.org/r/e9589141-cfeb-90cd-2d0e-83a62787239a@xxxxxxxxxxxx > Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > --- > > The previous conversation has given me enough clarity that I can see > which tests I am comfortable with use for this pending regression fix. > > I have tested this and it works for me. Does anyone have any concerns > with this change? I'd really love some kind of selftest that exercises the edge cases; do you have your tests in some form that could be converted? But otherwise, yes, this looks like the best option here. Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > kernel/user_namespace.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index 6b2e3ca7ee99..5481ba44a8d6 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -58,6 +58,18 @@ static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns) > cred->user_ns = user_ns; > } > > +static unsigned long enforced_nproc_rlimit(void) > +{ > + unsigned long limit = RLIM_INFINITY; > + > + /* Is RLIMIT_NPROC currently enforced? */ > + if (!uid_eq(current_uid(), GLOBAL_ROOT_UID) || > + (current_user_ns() != &init_user_ns)) > + limit = rlimit(RLIMIT_NPROC); > + > + return limit; > +} > + > /* > * Create a new user namespace, deriving the creator from the user in the > * passed credentials, and replacing that user with the new root user for the > @@ -122,7 +134,7 @@ int create_user_ns(struct cred *new) > for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) { > ns->ucount_max[i] = INT_MAX; > } > - set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)); > + set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_NPROC, enforced_nproc_rlimit()); > set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE)); > set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING)); > set_rlimit_ucount_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK)); > -- > 2.29.2 > -- Kees Cook
