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[PATCH 00/15] v2 kernel core refcount conversions

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  [PATCH 00/15] v2 kernel core refcount conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
    [PATCH 15/15] kernel: convert kcov.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
    [PATCH 07/15] kernel: convert ring_buffer.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
    [PATCH 08/15] kernel: convert ring_buffer.aux_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
    [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
      Re: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t  to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-07-07 11:40 +0200
        RE: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t  to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-07-07 12:20 +0200
    [PATCH 09/15] kernel: convert uprobe.ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:10 +0200
    [PATCH 05/15] kernel: convert task_struct.stack_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:20 +0200
    [PATCH 03/15] kernel: convert user_struct.__count from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-07-07 11:20 +0200

#1683053 — [PATCH 00/15] v2 kernel core refcount conversions

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.

If you want to test with refcount_t protection enabled, CONFIG_REFCOUNT_FULL
must be enabled.

* The respective change is currently merged into -next as
  "locking/refcount: Create unchecked atomic_t implementation".

Elena Reshetova (15):
  kernel: convert sighand_struct.count from atomic_t to refcount_t
  kernel: convert signal_struct.sigcnt from atomic_t to refcount_t
  kernel: convert user_struct.__count from atomic_t to refcount_t
  kernel: convert task_struct.usage from atomic_t to refcount_t
  kernel: convert task_struct.stack_refcount from atomic_t to refcount_t
  kernel: convert perf_event_context.refcount from atomic_t to
    refcount_t
  kernel: convert ring_buffer.refcount from atomic_t to refcount_t
  kernel: convert ring_buffer.aux_refcount from atomic_t to refcount_t
  kernel: convert uprobe.ref from atomic_t to refcount_t
  kernel: convert nsproxy.count from atomic_t to refcount_t
  kernel: convert group_info.usage from atomic_t to refcount_t
  kernel: convert cred.usage from atomic_t to refcount_t
  kernel: convert numa_group.refcount from atomic_t to refcount_t
  kernel: convert futex_pi_state.refcount from atomic_t to refcount_t
  kernel: convert kcov.refcount from atomic_t 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              |  8 +++----
 kernel/user.c                    |  8 +++----
 23 files changed, 110 insertions(+), 101 deletions(-)

-- 
2.7.4

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#1683054 — [PATCH 15/15] kernel: convert kcov.refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 kernel/kcov.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index cd77199..a6c7df3 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -19,6 +19,7 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/kcov.h>
+#include <linux/refcount.h>
 #include <asm/setup.h>
 
 /*
@@ -35,7 +36,7 @@ struct kcov {
 	 *  - opened file descriptor
 	 *  - task with enabled coverage (we can't unwire it from another task)
 	 */
-	atomic_t		refcount;
+	refcount_t		refcount;
 	/* The lock protects mode, size, area and t. */
 	spinlock_t		lock;
 	enum kcov_mode		mode;
@@ -94,12 +95,12 @@ EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
 
 static void kcov_get(struct kcov *kcov)
 {
-	atomic_inc(&kcov->refcount);
+	refcount_inc(&kcov->refcount);
 }
 
 static void kcov_put(struct kcov *kcov)
 {
-	if (atomic_dec_and_test(&kcov->refcount)) {
+	if (refcount_dec_and_test(&kcov->refcount)) {
 		vfree(kcov->area);
 		kfree(kcov);
 	}
@@ -175,7 +176,7 @@ static int kcov_open(struct inode *inode, struct file *filep)
 	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 	if (!kcov)
 		return -ENOMEM;
-	atomic_set(&kcov->refcount, 1);
+	refcount_set(&kcov->refcount, 1);
 	spin_lock_init(&kcov->lock);
 	filep->private_data = kcov;
 	return nonseekable_open(inode, filep);
-- 
2.7.4

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#1683055 — [PATCH 07/15] kernel: convert ring_buffer.refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 kernel/events/core.c        | 4 ++--
 kernel/events/internal.h    | 3 ++-
 kernel/events/ring_buffer.c | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 11d051f..890c3a8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5049,7 +5049,7 @@ struct ring_buffer *ring_buffer_get(struct perf_event *event)
 	rcu_read_lock();
 	rb = rcu_dereference(event->rb);
 	if (rb) {
-		if (!atomic_inc_not_zero(&rb->refcount))
+		if (!refcount_inc_not_zero(&rb->refcount))
 			rb = NULL;
 	}
 	rcu_read_unlock();
@@ -5059,7 +5059,7 @@ struct ring_buffer *ring_buffer_get(struct perf_event *event)
 
 void ring_buffer_put(struct ring_buffer *rb)
 {
-	if (!atomic_dec_and_test(&rb->refcount))
+	if (!refcount_dec_and_test(&rb->refcount))
 		return;
 
 	WARN_ON_ONCE(!list_empty(&rb->event_list));
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 486fd78..b8e6fdf 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -3,13 +3,14 @@
 
 #include <linux/hardirq.h>
 #include <linux/uaccess.h>
+#include <linux/refcount.h>
 
 /* Buffer handling */
 
 #define RING_BUFFER_WRITABLE		0x01
 
 struct ring_buffer {
-	atomic_t			refcount;
+	refcount_t			refcount;
 	struct rcu_head			rcu_head;
 #ifdef CONFIG_PERF_USE_VMALLOC
 	struct work_struct		work;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index ee97196..3353572 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -284,7 +284,7 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
 	else
 		rb->overwrite = 1;
 
-	atomic_set(&rb->refcount, 1);
+	refcount_set(&rb->refcount, 1);
 
 	INIT_LIST_HEAD(&rb->event_list);
 	spin_lock_init(&rb->event_lock);
-- 
2.7.4

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#1683056 — [PATCH 08/15] kernel: convert ring_buffer.aux_refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.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 890c3a8..aaea75b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5124,7 +5124,7 @@ 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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#1683059 — [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

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

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 008c514..6e5b714 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1130,7 +1130,7 @@ static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
 }
 
 struct numa_group {
-	atomic_t refcount;
+	refcount_t refcount;
 
 	spinlock_t lock; /* nr_tasks, tasks */
 	int nr_tasks;
@@ -2177,12 +2177,12 @@ 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);
 }
 
@@ -2203,7 +2203,7 @@ 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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#1683077 — Re: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to refcount_t

On Fri, Jul 07, 2017 at 12:04:27PM +0300, Elena Reshetova wrote:
> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: David Windsor <dwindsor@gmail.com>

Invalid SoB..

> Subject: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to refcount_t

> ---
>  kernel/sched/fair.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

Invalid Subject prefix too, scheduler patches get to have "sched:"

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#1683108 — RE: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to refcount_t

> On Fri, Jul 07, 2017 at 12:04:27PM +0300, Elena Reshetova wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > Signed-off-by: David Windsor <dwindsor@gmail.com>
> 
> Invalid SoB..
> 
> > Subject: [PATCH 13/15] kernel: convert numa_group.refcount from atomic_t to
> refcount_t
> 
> > ---
> >  kernel/sched/fair.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> Invalid Subject prefix too, scheduler patches get to have "sched:"

OK, will fix. 

Best Regards,
Elena.

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#1683060 — [PATCH 09/15] kernel: convert uprobe.ref from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.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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#1683063 — [PATCH 05/15] kernel: convert task_struct.stack_refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.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 348466a..96802198 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>
@@ -208,7 +209,7 @@ 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 6a01517..73be022 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1070,7 +1070,7 @@ 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 c549b0b..1e0e14e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -354,7 +354,7 @@ 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
@@ -372,7 +372,7 @@ 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);
@@ -532,7 +532,7 @@ 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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#1683064 — [PATCH 03/15] kernel: convert user_struct.__count from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 include/linux/sched/user.h | 5 +++--
 kernel/user.c              | 8 ++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 5d5415e..0a9953d 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -3,6 +3,7 @@
 
 #include <linux/uidgid.h>
 #include <linux/atomic.h>
+#include <linux/refcount.h>
 
 struct key;
 
@@ -10,7 +11,7 @@ struct key;
  * Some day this will be a full-fledged user tracking system..
  */
 struct user_struct {
-	atomic_t __count;	/* reference count */
+	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
@@ -53,7 +54,7 @@ extern struct user_struct root_user;
 extern struct user_struct * alloc_uid(kuid_t);
 static inline struct user_struct *get_uid(struct user_struct *u)
 {
-	atomic_inc(&u->__count);
+	refcount_inc(&u->__count);
 	return u;
 }
 extern void free_uid(struct user_struct *);
diff --git a/kernel/user.c b/kernel/user.c
index 00281ad..c072348 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -90,7 +90,7 @@ static DEFINE_SPINLOCK(uidhash_lock);
 
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
-	.__count	= ATOMIC_INIT(1),
+	.__count	= REFCOUNT_INIT(1),
 	.processes	= ATOMIC_INIT(1),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
@@ -116,7 +116,7 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 
 	hlist_for_each_entry(user, hashent, uidhash_node) {
 		if (uid_eq(user->uid, uid)) {
-			atomic_inc(&user->__count);
+			refcount_inc(&user->__count);
 			return user;
 		}
 	}
@@ -163,7 +163,7 @@ void free_uid(struct user_struct *up)
 		return;
 
 	local_irq_save(flags);
-	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
+	if (refcount_dec_and_lock(&up->__count, &uidhash_lock))
 		free_user(up, flags);
 	else
 		local_irq_restore(flags);
@@ -184,7 +184,7 @@ struct user_struct *alloc_uid(kuid_t uid)
 			goto out_unlock;
 
 		new->uid = uid;
-		atomic_set(&new->__count, 1);
+		refcount_set(&new->__count, 1);
 
 		/*
 		 * Before adding this, check whether we raced
-- 
2.7.4

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