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[PATCH 00/15] v4 kernel core pieces refcount conversions

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  [PATCH 00/15] v4 kernel core pieces refcount conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 04/15] sched: convert numa_group.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 09/15] perf/ring_buffer: convert ring_buffer.aux_refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 06/15] sched/task_struct: convert task_struct.stack_refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 10/15] uprobes: convert uprobe.ref to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 07/15] perf: convert perf_event_context.refcount to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 01/15] sched: convert sighand_struct.count to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200
    [PATCH 05/15] sched/task_struct: convert task_struct.usage to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-08-25 11:50 +0200

#1719894 — [PATCH 00/15] v4 kernel core pieces refcount conversions

Resending this with latest rebases.
Now we have at least x86 support for ARCH_HAS_REFCOUNT merged and
arm and others on their way.


Changes in v4:
 * just rebase and corrections on linux-next/master

Changes in v3:
 * SoB chain corrected
 * minor corrections based on v2 feedback
 * rebase on linux-next/master as of today

Changes in v2:
 * dropped already merged patches
 * rebase on top of linux-next/master
 * Now by default refcount_t = atomic_t (*) and uses all atomic
   standard operations unless CONFIG_REFCOUNT_FULL is enabled.
   This is a compromise for the systems that are critical on
   performance (such as net) and cannot accept even slight delay
   on the refcounter operations.

This series, for core kernel components, replaces atomic_t reference
counters with the new refcount_t type and API (see include/linux/refcount.h).
By doing this we prevent intentional or accidental
underflows or overflows that can led to use-after-free vulnerabilities.

The patches are fully independent and can be cherry-picked separately.
If there are no objections to the patches, please merge them via respective trees.


Elena Reshetova (15):
  sched: convert sighand_struct.count to refcount_t
  sched: convert signal_struct.sigcnt to refcount_t
  sched: convert user_struct.__count to refcount_t
  sched: convert numa_group.refcount to refcount_t
  sched/task_struct: convert task_struct.usage to refcount_t
  sched/task_struct: convert task_struct.stack_refcount to refcount_t
  perf: convert perf_event_context.refcount to refcount_t
  perf/ring_buffer: convert ring_buffer.refcount to refcount_t
  perf/ring_buffer: convert ring_buffer.aux_refcount to refcount_t
  uprobes: convert uprobe.ref to refcount_t
  nsproxy: convert nsproxy.count to refcount_t
  groups: convert group_info.usage to refcount_t
  creds: convert cred.usage to refcount_t
  futex: convert futex_pi_state.refcount to refcount_t
  kcov: convert kcov.refcount to refcount_t

 fs/exec.c                        |  4 ++--
 fs/proc/task_nommu.c             |  2 +-
 include/linux/cred.h             | 13 ++++++------
 include/linux/init_task.h        |  7 +++---
 include/linux/nsproxy.h          |  6 +++---
 include/linux/perf_event.h       |  3 ++-
 include/linux/sched.h            |  5 +++--
 include/linux/sched/signal.h     |  5 +++--
 include/linux/sched/task.h       |  4 ++--
 include/linux/sched/task_stack.h |  2 +-
 include/linux/sched/user.h       |  5 +++--
 kernel/cred.c                    | 46 ++++++++++++++++++++--------------------
 kernel/events/core.c             | 18 ++++++++--------
 kernel/events/internal.h         |  5 +++--
 kernel/events/ring_buffer.c      |  8 +++----
 kernel/events/uprobes.c          |  8 +++----
 kernel/fork.c                    | 24 ++++++++++-----------
 kernel/futex.c                   | 13 ++++++------
 kernel/groups.c                  |  2 +-
 kernel/kcov.c                    |  9 ++++----
 kernel/nsproxy.c                 |  6 +++---
 kernel/sched/fair.c              | 12 +++++------
 kernel/user.c                    |  8 +++----
 23 files changed, 112 insertions(+), 103 deletions(-)

-- 
2.7.4

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#1719895 — [PATCH 04/15] sched: convert numa_group.refcount to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable numa_group.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 kernel/sched/fair.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a5d83ed..fe4e38c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1059,7 +1059,7 @@ unsigned int sysctl_numa_balancing_scan_size = 256;
 unsigned int sysctl_numa_balancing_scan_delay = 1000;
 
 struct numa_group {
-	atomic_t refcount;
+	refcount_t refcount;
 
 	spinlock_t lock; /* nr_tasks, tasks */
 	int nr_tasks;
@@ -1128,7 +1128,7 @@ static unsigned int task_scan_start(struct task_struct *p)
 		unsigned long shared = group_faults_shared(ng);
 		unsigned long private = group_faults_priv(ng);
 
-		period *= atomic_read(&ng->refcount);
+		period *= refcount_read(&ng->refcount);
 		period *= shared + 1;
 		period /= private + shared + 1;
 	}
@@ -1151,7 +1151,7 @@ static unsigned int task_scan_max(struct task_struct *p)
 		unsigned long private = group_faults_priv(ng);
 		unsigned long period = smax;
 
-		period *= atomic_read(&ng->refcount);
+		period *= refcount_read(&ng->refcount);
 		period *= shared + 1;
 		period /= private + shared + 1;
 
@@ -2236,12 +2236,12 @@ static void task_numa_placement(struct task_struct *p)
 
 static inline int get_numa_group(struct numa_group *grp)
 {
-	return atomic_inc_not_zero(&grp->refcount);
+	return refcount_inc_not_zero(&grp->refcount);
 }
 
 static inline void put_numa_group(struct numa_group *grp)
 {
-	if (atomic_dec_and_test(&grp->refcount))
+	if (refcount_dec_and_test(&grp->refcount))
 		kfree_rcu(grp, rcu);
 }
 
@@ -2262,7 +2262,7 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 		if (!grp)
 			return;
 
-		atomic_set(&grp->refcount, 1);
+		refcount_set(&grp->refcount, 1);
 		grp->active_nodes = 1;
 		grp->max_faults_cpu = 0;
 		spin_lock_init(&grp->lock);
-- 
2.7.4

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#1719896 — [PATCH 09/15] perf/ring_buffer: convert ring_buffer.aux_refcount to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable ring_buffer.aux_refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 kernel/events/core.c        | 2 +-
 kernel/events/internal.h    | 2 +-
 kernel/events/ring_buffer.c | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4169469..031cb8e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5164,7 +5164,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
 
 		/* this has to be the last one */
 		rb_free_aux(rb);
-		WARN_ON_ONCE(atomic_read(&rb->aux_refcount));
+		WARN_ON_ONCE(refcount_read(&rb->aux_refcount));
 
 		mutex_unlock(&event->mmap_mutex);
 	}
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index b8e6fdf..fb55716 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -48,7 +48,7 @@ struct ring_buffer {
 	atomic_t			aux_mmap_count;
 	unsigned long			aux_mmap_locked;
 	void				(*free_aux)(void *);
-	atomic_t			aux_refcount;
+	refcount_t			aux_refcount;
 	void				**aux_pages;
 	void				*aux_priv;
 
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 3353572..ba12fd2 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -357,7 +357,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
 	if (!atomic_read(&rb->aux_mmap_count))
 		goto err;
 
-	if (!atomic_inc_not_zero(&rb->aux_refcount))
+	if (!refcount_inc_not_zero(&rb->aux_refcount))
 		goto err;
 
 	/*
@@ -648,7 +648,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
 	 * we keep a refcount here to make sure either of the two can
 	 * reference them safely.
 	 */
-	atomic_set(&rb->aux_refcount, 1);
+	refcount_set(&rb->aux_refcount, 1);
 
 	rb->aux_overwrite = overwrite;
 	rb->aux_watermark = watermark;
@@ -667,7 +667,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
 
 void rb_free_aux(struct ring_buffer *rb)
 {
-	if (atomic_dec_and_test(&rb->aux_refcount))
+	if (refcount_dec_and_test(&rb->aux_refcount))
 		__rb_free_aux(rb);
 }
 
-- 
2.7.4

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#1719897 — [PATCH 06/15] sched/task_struct: convert task_struct.stack_refcount to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable task_struct.stack_refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 include/linux/init_task.h        | 3 ++-
 include/linux/sched.h            | 2 +-
 include/linux/sched/task_stack.h | 2 +-
 kernel/fork.c                    | 6 +++---
 4 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index d312376..af2ebe6 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -12,6 +12,7 @@
 #include <linux/securebits.h>
 #include <linux/seqlock.h>
 #include <linux/rbtree.h>
+#include <linux/refcount.h>
 #include <linux/sched/autogroup.h>
 #include <net/net_namespace.h>
 #include <linux/sched/rt.h>
@@ -207,7 +208,7 @@ extern struct cred init_cred;
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 # define INIT_TASK_TI(tsk)			\
 	.thread_info = INIT_THREAD_INFO(tsk),	\
-	.stack_refcount = ATOMIC_INIT(1),
+	.stack_refcount = REFCOUNT_INIT(1),
 #else
 # define INIT_TASK_TI(tsk)
 #endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1eeb300..3d21012 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1089,7 +1089,7 @@ struct task_struct {
 #endif
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/* A live task holds one reference: */
-	atomic_t			stack_refcount;
+	refcount_t			stack_refcount;
 #endif
 #ifdef CONFIG_LIVEPATCH
 	int patch_state;
diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
index df6ea66..aab3809 100644
--- a/include/linux/sched/task_stack.h
+++ b/include/linux/sched/task_stack.h
@@ -60,7 +60,7 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 static inline void *try_get_task_stack(struct task_struct *tsk)
 {
-	return atomic_inc_not_zero(&tsk->stack_refcount) ?
+	return refcount_inc_not_zero(&tsk->stack_refcount) ?
 		task_stack_page(tsk) : NULL;
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 1e54683..4208c79 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -355,7 +355,7 @@ static void release_task_stack(struct task_struct *tsk)
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 void put_task_stack(struct task_struct *tsk)
 {
-	if (atomic_dec_and_test(&tsk->stack_refcount))
+	if (refcount_dec_and_test(&tsk->stack_refcount))
 		release_task_stack(tsk);
 }
 #endif
@@ -373,7 +373,7 @@ void free_task(struct task_struct *tsk)
 	 * If the task had a separate stack allocation, it should be gone
 	 * by now.
 	 */
-	WARN_ON_ONCE(atomic_read(&tsk->stack_refcount) != 0);
+	WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0);
 #endif
 	rt_mutex_debug_task_free(tsk);
 	ftrace_graph_exit_task(tsk);
@@ -535,7 +535,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	tsk->stack_vm_area = stack_vm_area;
 #endif
 #ifdef CONFIG_THREAD_INFO_IN_TASK
-	atomic_set(&tsk->stack_refcount, 1);
+	refcount_set(&tsk->stack_refcount, 1);
 #endif
 
 	if (err)
-- 
2.7.4

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#1719899 — [PATCH 10/15] uprobes: convert uprobe.ref to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable uprobe.ref is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 kernel/events/uprobes.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 456596d..ca093957 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem;
 
 struct uprobe {
 	struct rb_node		rb_node;	/* node in the rb tree */
-	atomic_t		ref;
+	refcount_t		ref;
 	struct rw_semaphore	register_rwsem;
 	struct rw_semaphore	consumer_rwsem;
 	struct list_head	pending_list;
@@ -371,13 +371,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
 
 static struct uprobe *get_uprobe(struct uprobe *uprobe)
 {
-	atomic_inc(&uprobe->ref);
+	refcount_inc(&uprobe->ref);
 	return uprobe;
 }
 
 static void put_uprobe(struct uprobe *uprobe)
 {
-	if (atomic_dec_and_test(&uprobe->ref))
+	if (refcount_dec_and_test(&uprobe->ref))
 		kfree(uprobe);
 }
 
@@ -459,7 +459,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
 	rb_link_node(&uprobe->rb_node, parent, p);
 	rb_insert_color(&uprobe->rb_node, &uprobes_tree);
 	/* get access + creation ref */
-	atomic_set(&uprobe->ref, 2);
+	refcount_set(&uprobe->ref, 2);
 
 	return u;
 }
-- 
2.7.4

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#1719900 — [PATCH 07/15] perf: convert perf_event_context.refcount to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable perf_event_context.refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 include/linux/perf_event.h |  3 ++-
 kernel/events/core.c       | 12 ++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9bac4bf..75c11181 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -54,6 +54,7 @@ struct perf_guest_info_callbacks {
 #include <linux/perf_regs.h>
 #include <linux/workqueue.h>
 #include <linux/cgroup.h>
+#include <linux/refcount.h>
 #include <asm/local.h>
 
 struct perf_callchain_entry {
@@ -737,7 +738,7 @@ struct perf_event_context {
 	int				nr_stat;
 	int				nr_freq;
 	int				rotate_disable;
-	atomic_t			refcount;
+	refcount_t			refcount;
 	struct task_struct		*task;
 
 	/*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 852768d..10ee0ea 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1109,7 +1109,7 @@ static void perf_event_ctx_deactivate(struct perf_event_context *ctx)
 
 static void get_ctx(struct perf_event_context *ctx)
 {
-	WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
+	refcount_inc(&ctx->refcount);
 }
 
 static void free_ctx(struct rcu_head *head)
@@ -1123,7 +1123,7 @@ static void free_ctx(struct rcu_head *head)
 
 static void put_ctx(struct perf_event_context *ctx)
 {
-	if (atomic_dec_and_test(&ctx->refcount)) {
+	if (refcount_dec_and_test(&ctx->refcount)) {
 		if (ctx->parent_ctx)
 			put_ctx(ctx->parent_ctx);
 		if (ctx->task && ctx->task != TASK_TOMBSTONE)
@@ -1201,7 +1201,7 @@ perf_event_ctx_lock_nested(struct perf_event *event, int nesting)
 again:
 	rcu_read_lock();
 	ctx = ACCESS_ONCE(event->ctx);
-	if (!atomic_inc_not_zero(&ctx->refcount)) {
+	if (!refcount_inc_not_zero(&ctx->refcount)) {
 		rcu_read_unlock();
 		goto again;
 	}
@@ -1329,7 +1329,7 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags)
 		}
 
 		if (ctx->task == TASK_TOMBSTONE ||
-		    !atomic_inc_not_zero(&ctx->refcount)) {
+		    !refcount_inc_not_zero(&ctx->refcount)) {
 			raw_spin_unlock(&ctx->lock);
 			ctx = NULL;
 		} else {
@@ -3795,7 +3795,7 @@ static void __perf_event_init_context(struct perf_event_context *ctx)
 	INIT_LIST_HEAD(&ctx->pinned_groups);
 	INIT_LIST_HEAD(&ctx->flexible_groups);
 	INIT_LIST_HEAD(&ctx->event_list);
-	atomic_set(&ctx->refcount, 1);
+	refcount_set(&ctx->refcount, 1);
 }
 
 static struct perf_event_context *
@@ -9812,7 +9812,7 @@ __perf_event_ctx_lock_double(struct perf_event *group_leader,
 again:
 	rcu_read_lock();
 	gctx = READ_ONCE(group_leader->ctx);
-	if (!atomic_inc_not_zero(&gctx->refcount)) {
+	if (!refcount_inc_not_zero(&gctx->refcount)) {
 		rcu_read_unlock();
 		goto again;
 	}
-- 
2.7.4

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#1719901 — [PATCH 01/15] sched: convert sighand_struct.count to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable sighand_struct.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 fs/exec.c                    | 4 ++--
 fs/proc/task_nommu.c         | 2 +-
 include/linux/init_task.h    | 2 +-
 include/linux/sched/signal.h | 3 ++-
 kernel/fork.c                | 8 ++++----
 5 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index daa19d8..5c8960d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1200,7 +1200,7 @@ static int de_thread(struct task_struct *tsk)
 	flush_itimer_signals();
 #endif
 
-	if (atomic_read(&oldsighand->count) != 1) {
+	if (refcount_read(&oldsighand->count) != 1) {
 		struct sighand_struct *newsighand;
 		/*
 		 * This ->sighand is shared with the CLONE_SIGHAND
@@ -1210,7 +1210,7 @@ static int de_thread(struct task_struct *tsk)
 		if (!newsighand)
 			return -ENOMEM;
 
-		atomic_set(&newsighand->count, 1);
+		refcount_set(&newsighand->count, 1);
 		memcpy(newsighand->action, oldsighand->action,
 		       sizeof(newsighand->action));
 
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 8652209..5038b6b 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -63,7 +63,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
 	else
 		bytes += kobjsize(current->files);
 
-	if (current->sighand && atomic_read(&current->sighand->count) > 1)
+	if (current->sighand && refcount_read(&current->sighand->count) > 1)
 		sbytes += kobjsize(current->sighand);
 	else
 		bytes += kobjsize(current->sighand);
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 3c07ace..6c6f520 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -85,7 +85,7 @@ extern struct fs_struct init_fs;
 extern struct nsproxy init_nsproxy;
 
 #define INIT_SIGHAND(sighand) {						\
-	.count		= ATOMIC_INIT(1), 				\
+	.count		= REFCOUNT_INIT(1), 				\
 	.action		= { { { .sa_handler = SIG_DFL, } }, },		\
 	.siglock	= __SPIN_LOCK_UNLOCKED(sighand.siglock),	\
 	.signalfd_wqh	= __WAIT_QUEUE_HEAD_INITIALIZER(sighand.signalfd_wqh),	\
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 2a0dd40..4d5cdf1 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -7,13 +7,14 @@
 #include <linux/sched/jobctl.h>
 #include <linux/sched/task.h>
 #include <linux/cred.h>
+#include <linux/refcount.h>
 
 /*
  * Types defining task->signal and task->sighand and APIs using them:
  */
 
 struct sighand_struct {
-	atomic_t		count;
+	refcount_t		count;
 	struct k_sigaction	action[_NSIG];
 	spinlock_t		siglock;
 	wait_queue_head_t	signalfd_wqh;
diff --git a/kernel/fork.c b/kernel/fork.c
index 8004fc7..43bcd20 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1320,7 +1320,7 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 	struct sighand_struct *sig;
 
 	if (clone_flags & CLONE_SIGHAND) {
-		atomic_inc(&current->sighand->count);
+		refcount_inc(&current->sighand->count);
 		return 0;
 	}
 	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
@@ -1328,14 +1328,14 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 	if (!sig)
 		return -ENOMEM;
 
-	atomic_set(&sig->count, 1);
+	refcount_set(&sig->count, 1);
 	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
 	return 0;
 }
 
 void __cleanup_sighand(struct sighand_struct *sighand)
 {
-	if (atomic_dec_and_test(&sighand->count)) {
+	if (refcount_dec_and_test(&sighand->count)) {
 		signalfd_cleanup(sighand);
 		/*
 		 * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it
@@ -2236,7 +2236,7 @@ static int check_unshare_flags(unsigned long unshare_flags)
 			return -EINVAL;
 	}
 	if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
-		if (atomic_read(&current->sighand->count) > 1)
+		if (refcount_read(&current->sighand->count) > 1)
 			return -EINVAL;
 	}
 	if (unshare_flags & CLONE_VM) {
-- 
2.7.4

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#1719902 — [PATCH 05/15] sched/task_struct: convert task_struct.usage to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable task_struct.usage is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
 include/linux/init_task.h  | 2 +-
 include/linux/sched.h      | 3 ++-
 include/linux/sched/task.h | 4 ++--
 kernel/fork.c              | 4 ++--
 4 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6c6f520..d312376 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -227,7 +227,7 @@ extern struct cred init_cred;
 	INIT_TASK_TI(tsk)						\
 	.state		= 0,						\
 	.stack		= init_stack,					\
-	.usage		= ATOMIC_INIT(2),				\
+	.usage		= REFCOUNT_INIT(2),				\
 	.flags		= PF_KTHREAD,					\
 	.prio		= MAX_PRIO-20,					\
 	.static_prio	= MAX_PRIO-20,					\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6110471..1eeb300 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -20,6 +20,7 @@
 #include <linux/seccomp.h>
 #include <linux/nodemask.h>
 #include <linux/rcupdate.h>
+#include <linux/refcount.h>
 #include <linux/resource.h>
 #include <linux/latencytop.h>
 #include <linux/sched/prio.h>
@@ -534,7 +535,7 @@ struct task_struct {
 	randomized_struct_fields_start
 
 	void				*stack;
-	atomic_t			usage;
+	refcount_t			usage;
 	/* Per task flags (PF_*), defined further below: */
 	unsigned int			flags;
 	unsigned int			ptrace;
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 79a2a74..2ddc9b0 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -85,13 +85,13 @@ extern void sched_exec(void);
 #define sched_exec()   {}
 #endif
 
-#define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0)
+#define get_task_struct(tsk) do { refcount_inc(&(tsk)->usage); } while(0)
 
 extern void __put_task_struct(struct task_struct *t);
 
 static inline void put_task_struct(struct task_struct *t)
 {
-	if (atomic_dec_and_test(&t->usage))
+	if (refcount_dec_and_test(&t->usage))
 		__put_task_struct(t);
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index d2e2eb0..1e54683 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -407,7 +407,7 @@ static inline void put_signal_struct(struct signal_struct *sig)
 void __put_task_struct(struct task_struct *tsk)
 {
 	WARN_ON(!tsk->exit_state);
-	WARN_ON(atomic_read(&tsk->usage));
+	WARN_ON(refcount_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
 	cgroup_free(tsk);
@@ -564,7 +564,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	 * One for us, one for whoever does the "release_task()" (usually
 	 * parent)
 	 */
-	atomic_set(&tsk->usage, 2);
+	refcount_set(&tsk->usage, 2);
 #ifdef CONFIG_BLK_DEV_IO_TRACE
 	tsk->btrace_seq = 0;
 #endif
-- 
2.7.4

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