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authorJoel Fernandes (Google) <joel@joelfernandes.org>2019-07-16 16:30:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-16 19:23:24 -0700
commitf57e515a1b56325a28a0972c632a623a9c84590c (patch)
tree62ec1f15fb12f43288b4246780642fbfa9c1c025 /include/linux/pid.h
parent156e0b1a8112b76e351684ac948c59757037ac36 (diff)
kernel/pid.c: 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. Link: http://lkml.kernel.org/r/20190701183826.191936-1-joel@joelfernandes.org Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: Jann Horn <jannh@google.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: KJ Tsanaktsidis <ktsanaktsidis@zendesk.com> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/pid.h')
-rw-r--r--include/linux/pid.h5
1 files changed, 3 insertions, 2 deletions
diff --git a/include/linux/pid.h b/include/linux/pid.h
index 1484db6ca8d1..2a83e434db9d 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -4,6 +4,7 @@
#include <linux/rculist.h>
#include <linux/wait.h>
+#include <linux/refcount.h>
enum pid_type
{
@@ -57,7 +58,7 @@ 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];
@@ -74,7 +75,7 @@ extern const struct file_operations pidfd_fops;
static inline struct pid *get_pid(struct pid *pid)
{
if (pid)
- atomic_inc(&pid->count);
+ refcount_inc(&pid->count);
return pid;
}