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Reimplement RLIMIT_NPROC on top of ucounts

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The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

To illustrate the impact of rlimits, let's say there is a program that
does not fork. Some service-A wants to run this program as user X in
multiple containers. Since the program never fork the service wants to
set RLIMIT_NPROC=1.

service-A
 \- program (uid=1000, container1, rlimit_nproc=1)
 \- program (uid=1000, container2, rlimit_nproc=1)

The service-A sets RLIMIT_NPROC=1 and runs the program in container1.
When the service-A tries to run a program with RLIMIT_NPROC=1 in
container2 it fails since user X already has one running process.

We cannot use existing inc_ucounts / dec_ucounts because they do not
allow us to exceed the maximum for the counter. Some rlimits can be
overlimited by root or if the user has the appropriate capability.

Changelog

v11:
* Change inc_rlimit_ucounts() which now returns top value of ucounts.
* Drop inc_rlimit_ucounts_and_test() because the return code of
  inc_rlimit_ucounts() can be checked.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/c5286a8aa16d2d698c222f7532f3d735c82bc6bc.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Alexey Gladkov
2021-04-22 14:27:11 +02:00
committed by Eric W. Biederman
parent b6c3365289
commit 21d1c5e386
11 changed files with 73 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/user_namespace.h
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@@ -50,9 +50,12 @@ enum ucount_type {
UCOUNT_INOTIFY_INSTANCES,
UCOUNT_INOTIFY_WATCHES,
#endif
UCOUNT_RLIMIT_NPROC,
UCOUNT_COUNTS,
};
#define MAX_PER_NAMESPACE_UCOUNTS UCOUNT_RLIMIT_NPROC
struct user_namespace {
struct uid_gid_map uid_map;
struct uid_gid_map gid_map;
@@ -110,6 +113,15 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
void put_ucounts(struct ucounts *ucounts);
static inline long get_ucounts_value(struct ucounts *ucounts, enum ucount_type type)
{
return atomic_long_read(&ucounts->ucount[type]);
}
long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max);
#ifdef CONFIG_USER_NS
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)