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Subject[PATCH] net: convert sk_filter.refcnt 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>
---
include/linux/filter.h | 3 ++-
net/core/filter.c | 7 ++++---
2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 8053c38..20247e7 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -7,6 +7,7 @@
#include <stdarg.h>

#include <linux/atomic.h>
+#include <linux/refcount.h>
#include <linux/compat.h>
#include <linux/skbuff.h>
#include <linux/linkage.h>
@@ -431,7 +432,7 @@ struct bpf_prog {
};

struct sk_filter {
- atomic_t refcnt;
+ refcount_t refcnt;
struct rcu_head rcu;
struct bpf_prog *prog;
};
diff --git a/net/core/filter.c b/net/core/filter.c
index ebaeaf2..62267e2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -928,7 +928,7 @@ static void sk_filter_release_rcu(struct rcu_head *rcu)
*/
static void sk_filter_release(struct sk_filter *fp)
{
- if (atomic_dec_and_test(&fp->refcnt))
+ if (refcount_dec_and_test(&fp->refcnt))
call_rcu(&fp->rcu, sk_filter_release_rcu);
}

@@ -950,7 +950,7 @@ bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
/* same check as in sock_kmalloc() */
if (filter_size <= sysctl_optmem_max &&
atomic_read(&sk->sk_omem_alloc) + filter_size < sysctl_optmem_max) {
- atomic_inc(&fp->refcnt);
+ refcount_inc(&fp->refcnt);
atomic_add(filter_size, &sk->sk_omem_alloc);
return true;
}
@@ -1179,12 +1179,13 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
return -ENOMEM;

fp->prog = prog;
- atomic_set(&fp->refcnt, 0);
+ refcount_set(&fp->refcnt, 1);

if (!sk_filter_charge(sk, fp)) {
kfree(fp);
return -ENOMEM;
}
+ refcount_set(&fp->refcnt, 1);

old_fp = rcu_dereference_protected(sk->sk_filter,
lockdep_sock_is_held(sk));
--
2.7.4
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