[Xen-devel] [PATCH 19/29] drivers, s390: convert lcs_reply.refcnt from atomic_t to refcount_t

[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.

Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 drivers/s390/net/lcs.c | 8 +++-----
 drivers/s390/net/lcs.h | 3 ++-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/net/lcs.c b/drivers/s390/net/lcs.c
index 211b31d..18dc787 100644
--- a/drivers/s390/net/lcs.c
+++ b/drivers/s390/net/lcs.c
@@ -774,15 +774,13 @@ lcs_get_lancmd(struct lcs_card *card, int count)
 static void
 lcs_get_reply(struct lcs_reply *reply)
 {
-       WARN_ON(atomic_read(&reply->refcnt) <= 0);
-       atomic_inc(&reply->refcnt);
+       refcount_inc(&reply->refcnt);
 }
 
 static void
 lcs_put_reply(struct lcs_reply *reply)
 {
-        WARN_ON(atomic_read(&reply->refcnt) <= 0);
-        if (atomic_dec_and_test(&reply->refcnt)) {
+        if (refcount_dec_and_test(&reply->refcnt)) {
                kfree(reply);
        }
 
@@ -798,7 +796,7 @@ lcs_alloc_reply(struct lcs_cmd *cmd)
        reply = kzalloc(sizeof(struct lcs_reply), GFP_ATOMIC);
        if (!reply)
                return NULL;
-       atomic_set(&reply->refcnt,1);
+       refcount_set(&reply->refcnt,1);
        reply->sequence_no = cmd->sequence_no;
        reply->received = 0;
        reply->rc = 0;
diff --git a/drivers/s390/net/lcs.h b/drivers/s390/net/lcs.h
index 150fcb4..3802f4f 100644
--- a/drivers/s390/net/lcs.h
+++ b/drivers/s390/net/lcs.h
@@ -4,6 +4,7 @@
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
 #include <linux/workqueue.h>
+#include <linux/refcount.h>
 #include <asm/ccwdev.h>
 
 #define LCS_DBF_TEXT(level, name, text) \
@@ -270,7 +271,7 @@ struct lcs_buffer {
 struct lcs_reply {
        struct list_head list;
        __u16 sequence_no;
-       atomic_t refcnt;
+       refcount_t refcnt;
        /* Callback for completion notification. */
        void (*callback)(struct lcs_card *, struct lcs_cmd *);
        wait_queue_head_t wait_q;
-- 
2.7.4


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