Re: [PATCH] net: convert sk_filter.refcnt from atomic_t to refcount_t

[Sergei Shtylyov]

Hello!

On 3/18/2017 3:58 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.reshet...@intel.com>
Signed-off-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: David Windsor <dwind...@gmail.com>

[...]

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

[...]

@@ -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);

   Why do it twice?

[...]

MBR, Sergei