bpf: export helper function flags and reject invalid ones

Export flags used by eBPF helper functions through UAPI, so they can be
used by programs (instead of them redefining all flags each time or just
using the hard-coded values). It also gives a better overview what flags
are used where and we can further get rid of the extra macros defined in
filter.c. Moreover, reject invalid flags.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -273,6 +273,22 @@ enum bpf_func_id {
 	__BPF_FUNC_MAX_ID,
 };
 
+/* All flags used by eBPF helper functions, placed here. */
+
+/* BPF_FUNC_skb_store_bytes flags. */
+#define BPF_F_RECOMPUTE_CSUM		(1ULL << 0)
+
+/* BPF_FUNC_l3_csum_replace and BPF_FUNC_l4_csum_replace flags.
+ * First 4 bits are for passing the header field size.
+ */
+#define BPF_F_HDR_FIELD_MASK		0xfULL
+
+/* BPF_FUNC_l4_csum_replace flags. */
+#define BPF_F_PSEUDO_HDR		(1ULL << 4)
+
+/* BPF_FUNC_clone_redirect and BPF_FUNC_redirect flags. */
+#define BPF_F_INGRESS			(1ULL << 0)
+
 /* user accessible mirror of in-kernel sk_buff.
  * new fields can only be added to the end of this structure
  */

net/core/filter.c

@@ -1328,8 +1328,7 @@ int sk_reuseport_attach_bpf(u32 ufd, struct sock *sk)
 	return 0;
 }
 
-#define BPF_RECOMPUTE_CSUM(flags)	((flags) & 1)
-#define BPF_LDST_LEN			16U
+#define BPF_LDST_LEN 16U
 
 static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 {
@@ -1340,6 +1339,9 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 	char buf[BPF_LDST_LEN];
 	void *ptr;
 
+	if (unlikely(flags & ~(BPF_F_RECOMPUTE_CSUM)))
+		return -EINVAL;
+
 	/* bpf verifier guarantees that:
 	 * 'from' pointer points to bpf program stack
 	 * 'len' bytes of it were initialized
@@ -1359,7 +1361,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 	if (unlikely(!ptr))
 		return -EFAULT;
 
-	if (BPF_RECOMPUTE_CSUM(flags))
+	if (flags & BPF_F_RECOMPUTE_CSUM)
 		skb_postpull_rcsum(skb, ptr, len);
 
 	memcpy(ptr, from, len);
@@ -1368,7 +1370,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 		/* skb_store_bits cannot return -EFAULT here */
 		skb_store_bits(skb, offset, ptr, len);
 
-	if (BPF_RECOMPUTE_CSUM(flags))
+	if (flags & BPF_F_RECOMPUTE_CSUM)
 		skb_postpush_rcsum(skb, ptr, len);
 
 	return 0;
@@ -1415,15 +1417,14 @@ const struct bpf_func_proto bpf_skb_load_bytes_proto = {
 	.arg4_type	= ARG_CONST_STACK_SIZE,
 };
 
-#define BPF_HEADER_FIELD_SIZE(flags)	((flags) & 0x0f)
-#define BPF_IS_PSEUDO_HEADER(flags)	((flags) & 0x10)
-
 static u64 bpf_l3_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 {
 	struct sk_buff *skb = (struct sk_buff *) (long) r1;
 	int offset = (int) r2;
 	__sum16 sum, *ptr;
 
+	if (unlikely(flags & ~(BPF_F_HDR_FIELD_MASK)))
+		return -EINVAL;
 	if (unlikely((u32) offset > 0xffff))
 		return -EFAULT;
 
@@ -1435,7 +1436,7 @@ static u64 bpf_l3_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 	if (unlikely(!ptr))
 		return -EFAULT;
 
-	switch (BPF_HEADER_FIELD_SIZE(flags)) {
+	switch (flags & BPF_F_HDR_FIELD_MASK) {
 	case 2:
 		csum_replace2(ptr, from, to);
 		break;
@@ -1467,10 +1468,12 @@ const struct bpf_func_proto bpf_l3_csum_replace_proto = {
 static u64 bpf_l4_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 {
 	struct sk_buff *skb = (struct sk_buff *) (long) r1;
-	bool is_pseudo = !!BPF_IS_PSEUDO_HEADER(flags);
+	bool is_pseudo = flags & BPF_F_PSEUDO_HDR;
 	int offset = (int) r2;
 	__sum16 sum, *ptr;
 
+	if (unlikely(flags & ~(BPF_F_PSEUDO_HDR | BPF_F_HDR_FIELD_MASK)))
+		return -EINVAL;
 	if (unlikely((u32) offset > 0xffff))
 		return -EFAULT;
 
@@ -1482,7 +1485,7 @@ static u64 bpf_l4_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 	if (unlikely(!ptr))
 		return -EFAULT;
 
-	switch (BPF_HEADER_FIELD_SIZE(flags)) {
+	switch (flags & BPF_F_HDR_FIELD_MASK) {
 	case 2:
 		inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo);
 		break;
@@ -1511,13 +1514,14 @@ const struct bpf_func_proto bpf_l4_csum_replace_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
-#define BPF_IS_REDIRECT_INGRESS(flags)	((flags) & 1)
-
 static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
 {
 	struct sk_buff *skb = (struct sk_buff *) (long) r1, *skb2;
 	struct net_device *dev;
 
+	if (unlikely(flags & ~(BPF_F_INGRESS)))
+		return -EINVAL;
+
 	dev = dev_get_by_index_rcu(dev_net(skb->dev), ifindex);
 	if (unlikely(!dev))
 		return -EINVAL;
@@ -1526,7 +1530,7 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
 	if (unlikely(!skb2))
 		return -ENOMEM;
 
-	if (BPF_IS_REDIRECT_INGRESS(flags)) {
+	if (flags & BPF_F_INGRESS) {
 		if (skb_at_tc_ingress(skb2))
 			skb_postpush_rcsum(skb2, skb_mac_header(skb2),
 					   skb2->mac_len);
@@ -1553,12 +1557,17 @@ struct redirect_info {
 };
 
 static DEFINE_PER_CPU(struct redirect_info, redirect_info);
+
 static u64 bpf_redirect(u64 ifindex, u64 flags, u64 r3, u64 r4, u64 r5)
 {
 	struct redirect_info *ri = this_cpu_ptr(&redirect_info);
 
+	if (unlikely(flags & ~(BPF_F_INGRESS)))
+		return TC_ACT_SHOT;
+
 	ri->ifindex = ifindex;
 	ri->flags = flags;
+
 	return TC_ACT_REDIRECT;
 }
 
@@ -1574,7 +1583,7 @@ int skb_do_redirect(struct sk_buff *skb)
 		return -EINVAL;
 	}
 
-	if (BPF_IS_REDIRECT_INGRESS(ri->flags)) {
+	if (ri->flags & BPF_F_INGRESS) {
 		if (skb_at_tc_ingress(skb))
 			skb_postpush_rcsum(skb, skb_mac_header(skb),
 					   skb->mac_len);