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authorDaniel Borkmann <daniel@iogearbox.net>2017-03-22 13:08:08 +0100
committerDavid S. Miller <davem@davemloft.net>2017-03-22 15:37:04 -0700
commita97e50cc4cb67e1e7bff56f6b41cda62ca832336 (patch)
treedb53d1b73380cd5f43813584fa948e401da052a6
parentc64c0b3cac4c5b8cb093727d2c19743ea3965c0b (diff)
downloadlinux-a97e50cc4cb67e1e7bff56f6b41cda62ca832336.tar.bz2
socket, bpf: fix sk_filter use after free in sk_clone_lock
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> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/core/sock.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/net/core/sock.c b/net/core/sock.c
index acb0d4137499..2c4f574168fb 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;