bpf: cleanup bpf_prog_run_{save,clear}_cb helpers
Move the details behind the cb[] access into a small helper to decouple
and make them generic for bpf_prog_run_save_cb()/bpf_prog_run_clear_cb()
that was introduced via commit ff936a04e5f2 ("bpf: fix cb access in socket
filter programs"). Also add a comment to better clarify what is done in
bpf_skb_cb().
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f5b5891..43aa1f8 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -350,25 +350,43 @@
#define BPF_PROG_RUN(filter, ctx) (*filter->bpf_func)(ctx, filter->insnsi)
+#define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
+
+static inline u8 *bpf_skb_cb(struct sk_buff *skb)
+{
+ /* eBPF programs may read/write skb->cb[] area to transfer meta
+ * data between tail calls. Since this also needs to work with
+ * tc, that scratch memory is mapped to qdisc_skb_cb's data area.
+ *
+ * In some socket filter cases, the cb unfortunately needs to be
+ * saved/restored so that protocol specific skb->cb[] data won't
+ * be lost. In any case, due to unpriviledged eBPF programs
+ * attached to sockets, we need to clear the bpf_skb_cb() area
+ * to not leak previous contents to user space.
+ */
+ BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) != BPF_SKB_CB_LEN);
+ BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) !=
+ FIELD_SIZEOF(struct qdisc_skb_cb, data));
+
+ return qdisc_skb_cb(skb)->data;
+}
+
static inline u32 bpf_prog_run_save_cb(const struct bpf_prog *prog,
struct sk_buff *skb)
{
- u8 *cb_data = qdisc_skb_cb(skb)->data;
- u8 saved_cb[QDISC_CB_PRIV_LEN];
+ u8 *cb_data = bpf_skb_cb(skb);
+ u8 cb_saved[BPF_SKB_CB_LEN];
u32 res;
- BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) !=
- QDISC_CB_PRIV_LEN);
-
if (unlikely(prog->cb_access)) {
- memcpy(saved_cb, cb_data, sizeof(saved_cb));
- memset(cb_data, 0, sizeof(saved_cb));
+ memcpy(cb_saved, cb_data, sizeof(cb_saved));
+ memset(cb_data, 0, sizeof(cb_saved));
}
res = BPF_PROG_RUN(prog, skb);
if (unlikely(prog->cb_access))
- memcpy(cb_data, saved_cb, sizeof(saved_cb));
+ memcpy(cb_data, cb_saved, sizeof(cb_saved));
return res;
}
@@ -376,10 +394,11 @@
static inline u32 bpf_prog_run_clear_cb(const struct bpf_prog *prog,
struct sk_buff *skb)
{
- u8 *cb_data = qdisc_skb_cb(skb)->data;
+ u8 *cb_data = bpf_skb_cb(skb);
if (unlikely(prog->cb_access))
- memset(cb_data, 0, QDISC_CB_PRIV_LEN);
+ memset(cb_data, 0, BPF_SKB_CB_LEN);
+
return BPF_PROG_RUN(prog, skb);
}