| Message ID | 3016fb20a3666f0db138b85049f9000ecd33a1f6.1490184193.git.daniel@iogearbox.net |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Daniel Borkmann <daniel@iogearbox.net> Date: Wed, 22 Mar 2017 13:08:08 +0100 > In sk_clone_lock(), we create a new socket and inherit most of the > parent's members via sock_copy() which memcpy()'s various sections. > Now, in case the parent socket had a BPF socket filter attached, > then newsk->sk_filter points to the same instance as the original > sk->sk_filter. > > sk_filter_charge() is then called on the newsk->sk_filter to take a > reference and should that fail due to hitting max optmem, we bail > out and release the newsk instance. > > The issue is that commit 278571baca2a ("net: filter: simplify socket > charging") wrongly combined the dismantle path with the failure path > of xfrm_sk_clone_policy(). This means, even when charging failed, we > call sk_free_unlock_clone() on the newsk, which then still points to > the same sk_filter as the original sk. > > Thus, sk_free_unlock_clone() calls into __sk_destruct() eventually > where it tests for present sk_filter and calls sk_filter_uncharge() > on it, which potentially lets sk_omem_alloc wrap around and releases > the eBPF prog and sk_filter structure from the (still intact) parent. > > Fix it by making sure that when sk_filter_charge() failed, we reset > newsk->sk_filter back to NULL before passing to sk_free_unlock_clone(), > so that we don't mess with the parents sk_filter. > > Only if xfrm_sk_clone_policy() fails, we did reach the point where > either the parent's filter was NULL and as a result newsk's as well > or where we previously had a successful sk_filter_charge(), thus for > that case, we do need sk_filter_uncharge() to release the prior taken > reference on sk_filter. > > Fixes: 278571baca2a ("net: filter: simplify socket charging") > Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> > Acked-by: Alexei Starovoitov <ast@kernel.org> Applied and queued up for -stable, thanks Daniel.
diff --git a/net/core/sock.c b/net/core/sock.c index acb0d41..2c4f574 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1544,6 +1544,12 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority) is_charged = sk_filter_charge(newsk, filter); if (unlikely(!is_charged || xfrm_sk_clone_policy(newsk, sk))) { + /* We need to make sure that we don't uncharge the new + * socket if we couldn't charge it in the first place + * as otherwise we uncharge the parent's filter. + */ + if (!is_charged) + RCU_INIT_POINTER(newsk->sk_filter, NULL); sk_free_unlock_clone(newsk); newsk = NULL; goto out;
In sk_clone_lock(), we create a new socket and inherit most of the parent's members via sock_copy() which memcpy()'s various sections. Now, in case the parent socket had a BPF socket filter attached, then newsk->sk_filter points to the same instance as the original sk->sk_filter. sk_filter_charge() is then called on the newsk->sk_filter to take a reference and should that fail due to hitting max optmem, we bail out and release the newsk instance. The issue is that commit 278571baca2a ("net: filter: simplify socket charging") wrongly combined the dismantle path with the failure path of xfrm_sk_clone_policy(). This means, even when charging failed, we call sk_free_unlock_clone() on the newsk, which then still points to the same sk_filter as the original sk. Thus, sk_free_unlock_clone() calls into __sk_destruct() eventually where it tests for present sk_filter and calls sk_filter_uncharge() on it, which potentially lets sk_omem_alloc wrap around and releases the eBPF prog and sk_filter structure from the (still intact) parent. Fix it by making sure that when sk_filter_charge() failed, we reset newsk->sk_filter back to NULL before passing to sk_free_unlock_clone(), so that we don't mess with the parents sk_filter. Only if xfrm_sk_clone_policy() fails, we did reach the point where either the parent's filter was NULL and as a result newsk's as well or where we previously had a successful sk_filter_charge(), thus for that case, we do need sk_filter_uncharge() to release the prior taken reference on sk_filter. Fixes: 278571baca2a ("net: filter: simplify socket charging") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> --- net/core/sock.c | 6 ++++++ 1 file changed, 6 insertions(+)