diff mbox series

[v11,4/9] Reimplement RLIMIT_NPROC on top of ucounts

Message ID c5286a8aa16d2d698c222f7532f3d735c82bc6bc.1619094428.git.legion@kernel.org (mailing list archive)
State New, archived
Headers show
Series Count rlimits in each user namespace | expand

Commit Message

Alexey Gladkov April 22, 2021, 12:27 p.m. UTC 
From: Alexey Gladkov <legion@kernel.org>

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>
---
 fs/exec.c                      |  2 +-
 include/linux/cred.h           |  2 ++
 include/linux/sched/user.h     |  1 -
 include/linux/user_namespace.h | 12 ++++++++++
 kernel/cred.c                  | 10 ++++----
 kernel/exit.c                  |  2 +-
 kernel/fork.c                  |  9 +++----
 kernel/sys.c                   |  2 +-
 kernel/ucount.c                | 44 ++++++++++++++++++++++++++++++++++
 kernel/user.c                  |  1 -
 kernel/user_namespace.c        |  3 ++-
 11 files changed, 73 insertions(+), 15 deletions(-)

Comments

Dan Carpenter April 29, 2021, 2:04 p.m. UTC | #1 
Hi,

url:    https://github.com/0day-ci/linux/commits/legion-kernel-org/Count-rlimits-in-each-user-namespace/20210427-162857
base:   https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next
config: arc-randconfig-m031-20210426 (attached as .config)
compiler: arceb-elf-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

smatch warnings:
kernel/ucount.c:270 dec_rlimit_ucounts() error: uninitialized symbol 'new'.

vim +/new +270 kernel/ucount.c

176ec2b092cc22 Alexey Gladkov 2021-04-22  260  bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
176ec2b092cc22 Alexey Gladkov 2021-04-22  261  {
176ec2b092cc22 Alexey Gladkov 2021-04-22  262  	struct ucounts *iter;
176ec2b092cc22 Alexey Gladkov 2021-04-22  263  	long new;
                                                ^^^^^^^^

176ec2b092cc22 Alexey Gladkov 2021-04-22  264  	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
176ec2b092cc22 Alexey Gladkov 2021-04-22  265  		long dec = atomic_long_add_return(-v, &iter->ucount[type]);
176ec2b092cc22 Alexey Gladkov 2021-04-22  266  		WARN_ON_ONCE(dec < 0);
176ec2b092cc22 Alexey Gladkov 2021-04-22  267  		if (iter == ucounts)
176ec2b092cc22 Alexey Gladkov 2021-04-22  268  			new = dec;
176ec2b092cc22 Alexey Gladkov 2021-04-22  269  	}
176ec2b092cc22 Alexey Gladkov 2021-04-22 @270  	return (new == 0);
                                                        ^^^^^^^^
I don't know if this is a bug or not, but I can definitely tell why the
static checker complains about it.

176ec2b092cc22 Alexey Gladkov 2021-04-22  271  }

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
diff mbox series

Patch

diff --git a/fs/exec.c b/fs/exec.c
index d7c4187ca023..f2bcdbeb3afb 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1878,7 +1878,7 @@  static int do_execveat_common(int fd, struct filename *filename,
 	 * whether NPROC limit is still exceeded.
 	 */
 	if ((current->flags & PF_NPROC_EXCEEDED) &&
-	    atomic_read(&current_user()->processes) > rlimit(RLIMIT_NPROC)) {
+	    is_ucounts_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
 		retval = -EAGAIN;
 		goto out_ret;
 	}
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 66436e655032..5ca1e8a1d035 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -372,6 +372,7 @@  static inline void put_cred(const struct cred *_cred)
 
 #define task_uid(task)		(task_cred_xxx((task), uid))
 #define task_euid(task)		(task_cred_xxx((task), euid))
+#define task_ucounts(task)	(task_cred_xxx((task), ucounts))
 
 #define current_cred_xxx(xxx)			\
 ({						\
@@ -388,6 +389,7 @@  static inline void put_cred(const struct cred *_cred)
 #define current_fsgid() 	(current_cred_xxx(fsgid))
 #define current_cap()		(current_cred_xxx(cap_effective))
 #define current_user()		(current_cred_xxx(user))
+#define current_ucounts()	(current_cred_xxx(ucounts))
 
 extern struct user_namespace init_user_ns;
 #ifdef CONFIG_USER_NS
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index a8ec3b6093fc..d33d867ad6c1 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -12,7 +12,6 @@ 
  */
 struct user_struct {
 	refcount_t __count;	/* reference count */
-	atomic_t processes;	/* How many processes does this user have? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_FANOTIFY
 	atomic_t fanotify_listeners;
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d84cc2c0b443..d5bb4abb8f3e 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -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;
@@ -107,6 +110,15 @@  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)
diff --git a/kernel/cred.c b/kernel/cred.c
index 58a8a9e24347..dcfa30b337c5 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -360,7 +360,7 @@  int copy_creds(struct task_struct *p, unsigned long clone_flags)
 		kdebug("share_creds(%p{%d,%d})",
 		       p->cred, atomic_read(&p->cred->usage),
 		       read_cred_subscribers(p->cred));
-		atomic_inc(&p->cred->user->processes);
+		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 		return 0;
 	}
 
@@ -395,8 +395,8 @@  int copy_creds(struct task_struct *p, unsigned long clone_flags)
 	}
 #endif
 
-	atomic_inc(&new->user->processes);
 	p->cred = p->real_cred = get_cred(new);
+	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	alter_cred_subscribers(new, 2);
 	validate_creds(new);
 	return 0;
@@ -496,12 +496,12 @@  int commit_creds(struct cred *new)
 	 * in set_user().
 	 */
 	alter_cred_subscribers(new, 2);
-	if (new->user != old->user)
-		atomic_inc(&new->user->processes);
+	if (new->user != old->user || new->user_ns != old->user_ns)
+		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	rcu_assign_pointer(task->real_cred, new);
 	rcu_assign_pointer(task->cred, new);
 	if (new->user != old->user)
-		atomic_dec(&old->user->processes);
+		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	alter_cred_subscribers(old, -2);
 
 	/* send notifications */
diff --git a/kernel/exit.c b/kernel/exit.c
index 04029e35e69a..61c0fe902b50 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -188,7 +188,7 @@  void release_task(struct task_struct *p)
 	/* don't need to get the RCU readlock here - the process is dead and
 	 * can't be modifying its own credentials. But shut RCU-lockdep up */
 	rcu_read_lock();
-	atomic_dec(&__task_cred(p)->user->processes);
+	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	rcu_read_unlock();
 
 	cgroup_release(p);
diff --git a/kernel/fork.c b/kernel/fork.c
index 37498cca6a1d..d8a4956463ae 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -819,9 +819,11 @@  void __init fork_init(void)
 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
 		init_task.signal->rlim[RLIMIT_NPROC];
 
-	for (i = 0; i < UCOUNT_COUNTS; i++)
+	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
 		init_user_ns.ucount_max[i] = max_threads/2;
 
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
+
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
 			  NULL, free_vm_stack_cache);
@@ -1972,8 +1974,7 @@  static __latent_entropy struct task_struct *copy_process(
 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
 #endif
 	retval = -EAGAIN;
-	if (atomic_read(&p->real_cred->user->processes) >=
-			task_rlimit(p, RLIMIT_NPROC)) {
+	if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
 		if (p->real_cred->user != INIT_USER &&
 		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
 			goto bad_fork_free;
@@ -2376,7 +2377,7 @@  static __latent_entropy struct task_struct *copy_process(
 #endif
 	delayacct_tsk_free(p);
 bad_fork_cleanup_count:
-	atomic_dec(&p->cred->user->processes);
+	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	exit_creds(p);
 bad_fork_free:
 	p->state = TASK_DEAD;
diff --git a/kernel/sys.c b/kernel/sys.c
index cabfc5b86175..00266a65a000 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -473,7 +473,7 @@  static int set_user(struct cred *new)
 	 * for programs doing set*uid()+execve() by harmlessly deferring the
 	 * failure to the execve() stage.
 	 */
-	if (atomic_read(&new_user->processes) >= rlimit(RLIMIT_NPROC) &&
+	if (is_ucounts_overlimit(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) &&
 			new_user != INIT_USER)
 		current->flags |= PF_NPROC_EXCEEDED;
 	else
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 365865f368ec..6caa56f7dec8 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -80,6 +80,7 @@  static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
 #endif
+	{ },
 	{ }
 };
 #endif /* CONFIG_SYSCTL */
@@ -240,6 +241,48 @@  void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 	put_ucounts(ucounts);
 }
 
+long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
+{
+	struct ucounts *iter;
+	long ret = 0;
+
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		long max = READ_ONCE(iter->ns->ucount_max[type]);
+		long new = atomic_long_add_return(v, &iter->ucount[type]);
+		if (new < 0 || new > max)
+			ret = LONG_MAX;
+		else if (iter == ucounts)
+			ret = new;
+	}
+	return ret;
+}
+
+bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
+{
+	struct ucounts *iter;
+	long new;
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		long dec = atomic_long_add_return(-v, &iter->ucount[type]);
+		WARN_ON_ONCE(dec < 0);
+		if (iter == ucounts)
+			new = dec;
+	}
+	return (new == 0);
+}
+
+bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max)
+{
+	struct ucounts *iter;
+	if (get_ucounts_value(ucounts, type) > max)
+		return true;
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		max = READ_ONCE(iter->ns->ucount_max[type]);
+		if (get_ucounts_value(iter, type) > max)
+			return true;
+	}
+	return false;
+}
+
 static __init int user_namespace_sysctl_init(void)
 {
 #ifdef CONFIG_SYSCTL
@@ -256,6 +299,7 @@  static __init int user_namespace_sysctl_init(void)
 	BUG_ON(!setup_userns_sysctls(&init_user_ns));
 #endif
 	hlist_add_ucounts(&init_ucounts);
+	inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	return 0;
 }
 subsys_initcall(user_namespace_sysctl_init);
diff --git a/kernel/user.c b/kernel/user.c
index a2478cddf536..7f5ff498207a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -98,7 +98,6 @@  static DEFINE_SPINLOCK(uidhash_lock);
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
 	.__count	= REFCOUNT_INIT(1),
-	.processes	= ATOMIC_INIT(1),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
 	.uid		= GLOBAL_ROOT_UID,
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 516db53166ab..2434b13b02e5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -118,9 +118,10 @@  int create_user_ns(struct cred *new)
 	ns->owner = owner;
 	ns->group = group;
 	INIT_WORK(&ns->work, free_user_ns);
-	for (i = 0; i < UCOUNT_COUNTS; i++) {
+	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) {
 		ns->ucount_max[i] = INT_MAX;
 	}
+	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */