From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
mathieu.desnoyers@efficios.com, willy@infradead.org,
peterz@infradead.org, will.deacon@arm.com,
paulmck@linux.vnet.ibm.com, elena.reshetova@intel.com,
keescook@chromium.org,
Andrea Parri <andrea.parri@amarulasolutions.com>,
kernel-team@android.com, kernel-hardening@lists.openwall.com,
jannh@google.com, Andrew Morton <akpm@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
KJ Tsanaktsidis <ktsanaktsidis@zendesk.com>,
Michal Hocko <mhocko@suse.com>
Subject: [PATCH v3] Convert struct pid count to refcount_t
Date: Mon, 1 Jul 2019 14:38:26 -0400 [thread overview]
Message-ID: <20190701183826.191936-1-joel@joelfernandes.org> (raw)
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@efficios.com
Cc: willy@infradead.org
Cc: peterz@infradead.org
Cc: will.deacon@arm.com
Cc: paulmck@linux.vnet.ibm.com
Cc: elena.reshetova@intel.com
Cc: keescook@chromium.org
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: kernel-team@android.com
Cc: kernel-hardening@lists.openwall.com
Cc: jannh@google.com
Reviewed-by: keescook@chromium.org
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.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
reply other threads:[~2019-07-01 18:38 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190701183826.191936-1-joel@joelfernandes.org \
--to=joel@joelfernandes.org \
--cc=akpm@linux-foundation.org \
--cc=andrea.parri@amarulasolutions.com \
--cc=ebiederm@xmission.com \
--cc=elena.reshetova@intel.com \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=kernel-hardening@lists.openwall.com \
--cc=kernel-team@android.com \
--cc=ktsanaktsidis@zendesk.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mhocko@suse.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=will.deacon@arm.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).