Kees Cook <keescook@xxxxxxxxxxxx> writes: > 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 Ahh... Typos. >> 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. Let's start with Michal Koutný tests. I keep forgetting to look at them. This cold has really been kicking my butt. For this issue the test case was a systemd unit file. Which is simple and demonstrates the real-world regression but not really minimal in the way a kernel selftest should be. > 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 >> Eric
