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net: convert lcs_reply.refcnt from atomic_t to refcount_t

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atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable lcs_reply.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <[email protected]>
Reviewed-by: David Windsor <[email protected]>
Reviewed-by: Hans Liljestrand <[email protected]>
Signed-off-by: Elena Reshetova <[email protected]>
[jwi: removed the WARN_ONs. Use CONFIG_REFCOUNT_FULL if you care.]
Signed-off-by: Julian Wiedmann <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Elena Reshetova 2017-12-20 20:10:55 +01:00 • committed by David S. Miller
commit c380cd5a00
2 changed files with 5 additions and 8 deletions
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10
drivers/s390/net/lcs.c
View file

@ -756,18 +756,14 @@ 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);
}
}
static struct lcs_reply *
@ -780,7 +776,7 @@ 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;

3
drivers/s390/net/lcs.h
View file

@ -5,6 +5,7 @@
#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) \
@ -271,7 +272,7 @@ 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;