[PATCH net-next 0/2] bpf: couple of fixes

[PATCH net-next 0/2] bpf: couple of fixes

[Daniel Borkmann]

These are two fixes for BPF, one to introduce xmit recursion limiter for
tc bpf programs and the other one to reject filters a bit earlier. For
more details please see individual patches. I have no strong opinion
to which tree they should go, they apply to both, but I think net-next
seems okay to me.

Thanks!

Daniel Borkmann (2):
  bpf: enforce recursion limit on redirects
  bpf: reject wrong sized filters earlier

 include/linux/netdevice.h |  2 ++
 net/core/dev.c            |  6 ++--
 net/core/filter.c         | 78 +++++++++++++++++++++++++++++------------------
 3 files changed, 53 insertions(+), 33 deletions(-)

-- 
1.9.3

[PATCH net-next 1/2] bpf: enforce recursion limit on redirects

[Daniel Borkmann]

Respect the stack's xmit_recursion limit for calls into dev_queue_xmit().
Currently, they are not handeled by the limiter when attached to clsact's
egress parent, for example, and a buggy program redirecting it to the
same device again could run into stack overflow eventually. It would be
good if we could notify an admin to give him a chance to react. We reuse
xmit_recursion instead of having one private to eBPF, so that the stack's
current recursion depth will be taken into account as well. Follow-up to
commit 3896d655f4d4 ("bpf: introduce bpf_clone_redirect() helper") and
27b29f63058d ("bpf: add bpf_redirect() helper").

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/netdevice.h |  2 ++
 net/core/dev.c            |  6 ++----
 net/core/filter.c         | 55 +++++++++++++++++++++++++++++------------------
 3 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4f234b1..94eef35 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2389,6 +2389,8 @@ void synchronize_net(void);
 int init_dummy_netdev(struct net_device *dev);
 
 DECLARE_PER_CPU(int, xmit_recursion);
+#define XMIT_RECURSION_LIMIT	10
+
 static inline int dev_recursion_level(void)
 {
 	return this_cpu_read(xmit_recursion);
diff --git a/net/core/dev.c b/net/core/dev.c
index c43c9d2..b148357 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3144,8 +3144,6 @@ static void skb_update_prio(struct sk_buff *skb)
 DEFINE_PER_CPU(int, xmit_recursion);
 EXPORT_SYMBOL(xmit_recursion);
 
-#define RECURSION_LIMIT 10
-
 /**
  *	dev_loopback_xmit - loop back @skb
  *	@net: network namespace this loopback is happening in
@@ -3388,8 +3386,8 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv)
 		int cpu = smp_processor_id(); /* ok because BHs are off */
 
 		if (txq->xmit_lock_owner != cpu) {
-
-			if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+			if (unlikely(__this_cpu_read(xmit_recursion) >
+				     XMIT_RECURSION_LIMIT))
 				goto recursion_alert;
 
 			skb = validate_xmit_skb(skb, dev);
diff --git a/net/core/filter.c b/net/core/filter.c
index 68adb5f..d11744d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1603,9 +1603,36 @@ static const struct bpf_func_proto bpf_csum_diff_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
+static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
+{
+	if (skb_at_tc_ingress(skb))
+		skb_postpush_rcsum(skb, skb_mac_header(skb), skb->mac_len);
+
+	return dev_forward_skb(dev, skb);
+}
+
+static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
+{
+	int ret;
+
+	if (unlikely(__this_cpu_read(xmit_recursion) > XMIT_RECURSION_LIMIT)) {
+		net_crit_ratelimited("bpf: recursion limit reached on datapath, buggy bpf program?\n");
+		kfree_skb(skb);
+		return -ENETDOWN;
+	}
+
+	skb->dev = dev;
+
+	__this_cpu_inc(xmit_recursion);
+	ret = dev_queue_xmit(skb);
+	__this_cpu_dec(xmit_recursion);
+
+	return ret;
+}
+
 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 sk_buff *skb = (struct sk_buff *) (long) r1;
 	struct net_device *dev;
 
 	if (unlikely(flags & ~(BPF_F_INGRESS)))
@@ -1615,19 +1642,12 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
 	if (unlikely(!dev))
 		return -EINVAL;
 
-	skb2 = skb_clone(skb, GFP_ATOMIC);
-	if (unlikely(!skb2))
+	skb = skb_clone(skb, GFP_ATOMIC);
+	if (unlikely(!skb))
 		return -ENOMEM;
 
-	if (flags & BPF_F_INGRESS) {
-		if (skb_at_tc_ingress(skb2))
-			skb_postpush_rcsum(skb2, skb_mac_header(skb2),
-					   skb2->mac_len);
-		return dev_forward_skb(dev, skb2);
-	}
-
-	skb2->dev = dev;
-	return dev_queue_xmit(skb2);
+	return flags & BPF_F_INGRESS ?
+	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);
 }
 
 static const struct bpf_func_proto bpf_clone_redirect_proto = {
@@ -1671,15 +1691,8 @@ int skb_do_redirect(struct sk_buff *skb)
 		return -EINVAL;
 	}
 
-	if (ri->flags & BPF_F_INGRESS) {
-		if (skb_at_tc_ingress(skb))
-			skb_postpush_rcsum(skb, skb_mac_header(skb),
-					   skb->mac_len);
-		return dev_forward_skb(dev, skb);
-	}
-
-	skb->dev = dev;
-	return dev_queue_xmit(skb);
+	return ri->flags & BPF_F_INGRESS ?
+	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);
 }
 
 static const struct bpf_func_proto bpf_redirect_proto = {
-- 
1.9.3

[PATCH net-next 2/2] bpf: reject wrong sized filters earlier

[Daniel Borkmann]

Add a bpf_check_basics_ok() and reject filters that are of invalid
size much earlier, so we don't do any useless work such as invoking
bpf_prog_alloc(). Currently, rejection happens in bpf_check_classic()
only, but it's really unnecessarily late and they should be rejected
at earliest point. While at it, also clean up one bpf_prog_size() to
make it consistent with the remaining invocations.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 net/core/filter.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index d11744d..df6860c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -748,6 +748,17 @@ static bool chk_code_allowed(u16 code_to_probe)
 	return codes[code_to_probe];
 }
 
+static bool bpf_check_basics_ok(const struct sock_filter *filter,
+				unsigned int flen)
+{
+	if (filter == NULL)
+		return false;
+	if (flen == 0 || flen > BPF_MAXINSNS)
+		return false;
+
+	return true;
+}
+
 /**
  *	bpf_check_classic - verify socket filter code
  *	@filter: filter to verify
@@ -768,9 +779,6 @@ static int bpf_check_classic(const struct sock_filter *filter,
 	bool anc_found;
 	int pc;
 
-	if (flen == 0 || flen > BPF_MAXINSNS)
-		return -EINVAL;
-
 	/* Check the filter code now */
 	for (pc = 0; pc < flen; pc++) {
 		const struct sock_filter *ftest = &filter[pc];
@@ -1065,7 +1073,7 @@ int bpf_prog_create(struct bpf_prog **pfp, struct sock_fprog_kern *fprog)
 	struct bpf_prog *fp;
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return -EINVAL;
 
 	fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
@@ -1112,7 +1120,7 @@ int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog,
 	int err;
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return -EINVAL;
 
 	fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
@@ -1207,7 +1215,6 @@ static
 struct bpf_prog *__get_filter(struct sock_fprog *fprog, struct sock *sk)
 {
 	unsigned int fsize = bpf_classic_proglen(fprog);
-	unsigned int bpf_fsize = bpf_prog_size(fprog->len);
 	struct bpf_prog *prog;
 	int err;
 
@@ -1215,10 +1222,10 @@ struct bpf_prog *__get_filter(struct sock_fprog *fprog, struct sock *sk)
 		return ERR_PTR(-EPERM);
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return ERR_PTR(-EINVAL);
 
-	prog = bpf_prog_alloc(bpf_fsize, 0);
+	prog = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
 	if (!prog)
 		return ERR_PTR(-ENOMEM);
 
-- 
1.9.3

Re: [PATCH net-next 0/2] bpf: couple of fixes

[David Miller]

From: Daniel Borkmann <daniel@iogearbox.net>
Date: Fri, 10 Jun 2016 21:19:05 +0200

> These are two fixes for BPF, one to introduce xmit recursion limiter for
> tc bpf programs and the other one to reject filters a bit earlier. For
> more details please see individual patches. I have no strong opinion
> to which tree they should go, they apply to both, but I think net-next
> seems okay to me.

Series applied to net-next, thanks Daniel.