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Subject[PATCH] Convert struct pid count to refcount_t
Date
struct pid's count is an atomic_t field used as a refcount. Use
refcount_t for it which is basically atomic_t but does additional
checking to prevent use-after-free bugs. No change in behavior if
CONFIG_REFCOUNT_FULL=n.

Cc: keescook@chromium.org
Cc: kernel-team@android.com
Cc: kernel-hardening@lists.openwall.com
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

---
include/linux/pid.h | 5 +++--
kernel/pid.c | 8 ++++----
2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 14a9a39da9c7..8cb86d377ff5 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -3,6 +3,7 @@
#define _LINUX_PID_H

#include <linux/rculist.h>
+#include <linux/refcount.h>

enum pid_type
{
@@ -56,7 +57,7 @@ struct upid {

struct pid
{
- atomic_t count;
+ refcount_t count;
unsigned int level;
/* lists of tasks that use this pid */
struct hlist_head tasks[PIDTYPE_MAX];
@@ -69,7 +70,7 @@ extern struct pid init_struct_pid;
static inline struct pid *get_pid(struct pid *pid)
{
if (pid)
- atomic_inc(&pid->count);
+ refcount_inc(&pid->count);
return pid;
}

diff --git a/kernel/pid.c b/kernel/pid.c
index 20881598bdfa..2095c7da644d 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -37,7 +37,7 @@
#include <linux/init_task.h>
#include <linux/syscalls.h>
#include <linux/proc_ns.h>
-#include <linux/proc_fs.h>
+#include <linux/refcount.h>
#include <linux/sched/task.h>
#include <linux/idr.h>

@@ -106,8 +106,8 @@ void put_pid(struct pid *pid)
return;

ns = pid->numbers[pid->level].ns;
- if ((atomic_read(&pid->count) == 1) ||
- atomic_dec_and_test(&pid->count)) {
+ if ((refcount_read(&pid->count) == 1) ||
+ refcount_dec_and_test(&pid->count)) {
kmem_cache_free(ns->pid_cachep, pid);
put_pid_ns(ns);
}
@@ -210,7 +210,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
}

get_pid_ns(ns);
- atomic_set(&pid->count, 1);
+ refcount_set(&pid->count, 1);
for (type = 0; type < PIDTYPE_MAX; ++type)
INIT_HLIST_HEAD(&pid->tasks[type]);

--
2.21.0.392.gf8f6787159e-goog
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