On 03/16/2017 04:28 PM, Elena Reshetova wrote:
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>
---
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);
Regarding the two subsequent refcount_set(, 1) that look a bit strange
due to the sk_filter_charge() having refcount_inc() I presume ... can't
the refcount API handle such corner case? Or alternatively the let the
sk_filter_charge() handle it, for example:
bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)
{
u32 filter_size = bpf_prog_size(fp->prog->len);
/* same check as in sock_kmalloc() */
if (filter_size <= sysctl_optmem_max &&
atomic_read(&sk->sk_omem_alloc) + filter_size < sysctl_optmem_max) {
atomic_add(filter_size, &sk->sk_omem_alloc);
return true;
}
return false;
}
And this goes to filter.h:
bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp);
bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
{
bool ret = __sk_filter_charge(sk, fp);
if (ret)
refcount_inc(&fp->refcnt);
return ret;
}
... and let __sk_attach_prog() call __sk_filter_charge() and only fo
the second refcount_set()?
old_fp = rcu_dereference_protected(sk->sk_filter,
lockdep_sock_is_held(sk));
