[PATCH v2] ipc: Convert ipc_kern_perm.refcount to refcount_t

From: Kees Cook
Date: Sat May 27 2017 - 20:40:29 EST


From: Elena Reshetova <elena.reshetova@xxxxxxxxx>

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.

Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Brown paper bag update: forgot to commit a missing hunk...
---
include/linux/ipc.h | 3 ++-
ipc/util.c | 6 +++---
2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 5591f055e13f..a7fecbc647d8 100644
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -3,6 +3,7 @@

#include <linux/spinlock.h>
#include <linux/uidgid.h>
+#include <linux/refcount.h>
#include <uapi/linux/ipc.h>

#define IPCMNI 32768 /* <= MAX_INT limit for ipc arrays (including sysctl changes) */
@@ -22,7 +23,7 @@ struct kern_ipc_perm {
void *security;

struct rcu_head rcu;
- atomic_t refcount;
+ refcount_t refcount;
} ____cacheline_aligned_in_smp;

#endif /* _LINUX_IPC_H */
diff --git a/ipc/util.c b/ipc/util.c
index 1a2cb02467ab..069bb22c9f64 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -232,7 +232,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)

idr_preload(GFP_KERNEL);

- atomic_set(&new->refcount, 1);
+ refcount_set(&new->refcount, 1);
spin_lock_init(&new->lock);
new->deleted = false;
rcu_read_lock();
@@ -397,13 +397,13 @@ void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)

int ipc_rcu_getref(struct kern_ipc_perm *ptr)
{
- return atomic_inc_not_zero(&ptr->refcount);
+ return refcount_inc_not_zero(&ptr->refcount);
}

void ipc_rcu_putref(struct kern_ipc_perm *ptr,
void (*func)(struct rcu_head *head))
{
- if (!atomic_dec_and_test(&ptr->refcount))
+ if (!refcount_dec_and_test(&ptr->refcount))
return;

call_rcu(&ptr->rcu, func);
--
2.7.4


--
Kees Cook
Pixel Security