bpf: fix cb access in socket filter programs

eBPF socket filter programs may see junk in 'u32 cb[5]' area,
since it could have been used by protocol layers earlier.

For socket filter programs used in af_packet we need to clean
20 bytes of skb->cb area if it could be used by the program.
For programs attached to TCP/UDP sockets we need to save/restore
these 20 bytes, since it's used by protocol layers.

Remove SK_RUN_FILTER macro, since it's no longer used.

Long term we may move this bpf cb area to per-cpu scratch, but that
requires addition of new 'per-cpu load/store' instructions,
so not suitable as a short term fix.

Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 5 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 342e6c8fc415..5f4cf1cffed3 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -56,10 +56,10 @@
  *	@sk: sock associated with &sk_buff
  *	@skb: buffer to filter
  *
- * Run the filter code and then cut skb->data to correct size returned by
- * SK_RUN_FILTER. If pkt_len is 0 we toss packet. If skb->len is smaller
+ * Run the eBPF program and then cut skb->data to correct size returned by
+ * the program. If pkt_len is 0 we toss packet. If skb->len is smaller
  * than pkt_len we keep whole skb->data. This is the socket level
- * wrapper to SK_RUN_FILTER. It returns 0 if the packet should
+ * wrapper to BPF_PROG_RUN. It returns 0 if the packet should
  * be accepted or -EPERM if the packet should be tossed.
  *
  */
@@ -83,7 +83,7 @@ int sk_filter(struct sock *sk, struct sk_buff *skb)
 	rcu_read_lock();
 	filter = rcu_dereference(sk->sk_filter);
 	if (filter) {
-		unsigned int pkt_len = SK_RUN_FILTER(filter, skb);
+		unsigned int pkt_len = bpf_prog_run_save_cb(filter->prog, skb);
 
 		err = pkt_len ? pskb_trim(skb, pkt_len) : -EPERM;
 	}
@@ -1736,7 +1736,8 @@ static bool tc_cls_act_is_valid_access(int off, int size,
 
 static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
 				      int src_reg, int ctx_off,
-				      struct bpf_insn *insn_buf)
+				      struct bpf_insn *insn_buf,
+				      struct bpf_prog *prog)
 {
 	struct bpf_insn *insn = insn_buf;
 
@@ -1827,6 +1828,7 @@ static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
 		offsetof(struct __sk_buff, cb[4]):
 		BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, data) < 20);
 
+		prog->cb_access = 1;
 		ctx_off -= offsetof(struct __sk_buff, cb[0]);
 		ctx_off += offsetof(struct sk_buff, cb);
 		ctx_off += offsetof(struct qdisc_skb_cb, data);