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Date: Mon, 1 Jul 2019 14:38:26 -0400
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
mathieu.desnoyers@...icios.com,
willy@...radead.org,
peterz@...radead.org,
will.deacon@....com,
paulmck@...ux.vnet.ibm.com,
elena.reshetova@...el.com,
keescook@...omium.org,
Andrea Parri <andrea.parri@...rulasolutions.com>,
kernel-team@...roid.com,
kernel-hardening@...ts.openwall.com,
jannh@...gle.com,
Andrew Morton <akpm@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
KJ Tsanaktsidis <ktsanaktsidis@...desk.com>,
Michal Hocko <mhocko@...e.com>
Subject: [PATCH v3] Convert struct pid count to refcount_t
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.
For memory ordering, the only change is with the following:
- if ((atomic_read(&pid->count) == 1) ||
- atomic_dec_and_test(&pid->count)) {
+ if (refcount_dec_and_test(&pid->count)) {
kmem_cache_free(ns->pid_cachep, pid);
Here the change is from:
Fully ordered --> RELEASE + ACQUIRE (as per refcount-vs-atomic.rst)
This ACQUIRE should take care of making sure the free happens after the
refcount_dec_and_test().
The above hunk also removes atomic_read() since it is not needed for the
code to work and it is unclear how beneficial it is. The removal lets
refcount_dec_and_test() check for cases where get_pid() happened before
the object was freed.
Cc: mathieu.desnoyers@...icios.com
Cc: willy@...radead.org
Cc: peterz@...radead.org
Cc: will.deacon@....com
Cc: paulmck@...ux.vnet.ibm.com
Cc: elena.reshetova@...el.com
Cc: keescook@...omium.org
Cc: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: kernel-team@...roid.com
Cc: kernel-hardening@...ts.openwall.com
Cc: jannh@...gle.com
Reviewed-by: keescook@...omium.org
Reviewed-by: Andrea Parri <andrea.parri@...rulasolutions.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
v1->v2 is to get rid of the atomic_read().
v2->v3 replaces ATOMIC_INIT with REFCOUNT_INIT
include/linux/pid.h | 5 +++--
kernel/pid.c | 9 ++++-----
2 files changed, 7 insertions(+), 7 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..86b526bd59e1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -37,12 +37,12 @@
#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>
struct pid init_struct_pid = {
- .count = ATOMIC_INIT(1),
+ .count = REFCOUNT_INIT(1),
.tasks = {
{ .first = NULL },
{ .first = NULL },
@@ -106,8 +106,7 @@ 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_dec_and_test(&pid->count)) {
kmem_cache_free(ns->pid_cachep, pid);
put_pid_ns(ns);
}
@@ -210,7 +209,7 @@ 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]);
--
2.22.0.410.gd8fdbe21b5-goog
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