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Subject[PATCH 17/17] net: convert packet_fanout.sk_ref from atomic_t to refcount_t
Date
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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
net/packet/af_packet.c | 8 ++++----
net/packet/internal.h | 4 +++-
2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 643302b..e3beb28 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1739,7 +1739,7 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
match->flags = flags;
INIT_LIST_HEAD(&match->list);
spin_lock_init(&match->lock);
- atomic_set(&match->sk_ref, 0);
+ refcount_set(&match->sk_ref, 0);
fanout_init_data(match);
match->prot_hook.type = po->prot_hook.type;
match->prot_hook.dev = po->prot_hook.dev;
@@ -1753,10 +1753,10 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
match->prot_hook.type == po->prot_hook.type &&
match->prot_hook.dev == po->prot_hook.dev) {
err = -ENOSPC;
- if (atomic_read(&match->sk_ref) < PACKET_FANOUT_MAX) {
+ if (refcount_read(&match->sk_ref) < PACKET_FANOUT_MAX) {
__dev_remove_pack(&po->prot_hook);
po->fanout = match;
- atomic_inc(&match->sk_ref);
+ refcount_set(&match->sk_ref, refcount_read(&match->sk_ref) + 1);
__fanout_link(sk, po);
err = 0;
}
@@ -1785,7 +1785,7 @@ static struct packet_fanout *fanout_release(struct sock *sk)
if (f) {
po->fanout = NULL;

- if (atomic_dec_and_test(&f->sk_ref))
+ if (refcount_dec_and_test(&f->sk_ref))
list_del(&f->list);
else
f = NULL;
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 9ee4631..94d1d40 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -1,6 +1,8 @@
#ifndef __PACKET_INTERNAL_H__
#define __PACKET_INTERNAL_H__

+#include <linux/refcount.h>
+
struct packet_mclist {
struct packet_mclist *next;
int ifindex;
@@ -86,7 +88,7 @@ struct packet_fanout {
struct list_head list;
struct sock *arr[PACKET_FANOUT_MAX];
spinlock_t lock;
- atomic_t sk_ref;
+ refcount_t sk_ref;
struct packet_type prot_hook ____cacheline_aligned_in_smp;
};

--
2.7.4
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