[PATCH v2 net-next 2/2] net: filter: split BPF out of core networking

[Alexei Starovoitov <ast@plumgrid.com>]

seccomp selects BPF only instead of whole NET
Other BPF users (like tracing filters) will select BPF only too

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
 arch/Kconfig      |    6 +++++-
 kernel/Makefile   |    2 +-
 kernel/bpf/core.c |   21 +++++++++++++++++++++
 net/Kconfig       |    1 +
 4 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 97ff872c7acc..d60637a29ea0 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -324,7 +324,8 @@ config HAVE_ARCH_SECCOMP_FILTER
 
 config SECCOMP_FILTER
 	def_bool y
-	depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
+	depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP
+	select BPF
 	help
 	  Enable tasks to build secure computing environments defined
 	  in terms of Berkeley Packet Filter programs which implement
@@ -332,6 +333,9 @@ config SECCOMP_FILTER
 
 	  See Documentation/prctl/seccomp_filter.txt for details.
 
+config BPF
+	boolean
+
 config HAVE_CC_STACKPROTECTOR
 	bool
 	help
diff --git a/kernel/Makefile b/kernel/Makefile
index e7360b7c2c0e..d5d7d0c18f36 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -87,7 +87,7 @@ obj-$(CONFIG_RING_BUFFER) += trace/
 obj-$(CONFIG_TRACEPOINTS) += trace/
 obj-$(CONFIG_IRQ_WORK) += irq_work.o
 obj-$(CONFIG_CPU_PM) += cpu_pm.o
-obj-$(CONFIG_NET) += bpf/
+obj-$(CONFIG_BPF) += bpf/
 
 obj-$(CONFIG_PERF_EVENTS) += events/
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 22c2d99414c0..8ca1b37ddc28 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1040,3 +1040,24 @@ void sk_filter_free(struct sk_filter *fp)
 	bpf_jit_free(fp);
 }
 EXPORT_SYMBOL_GPL(sk_filter_free);
+
+/* kernel configuration that do not enable NET are not using
+ * classic BPF extensions
+ */
+bool __weak sk_convert_bpf_extensions(struct sock_filter *fp,
+				      struct sock_filter_int **insnp)
+{
+	return false;
+}
+
+/* To emulate LD_ABS/LD_IND instructions __sk_run_filter() may call
+ * skb_copy_bits(), so provide a weak definition for it in NET-less config.
+ * seccomp_check_filter() verifies that seccomp filters are not using
+ * LD_ABS/LD_IND instructions. Other BPF users (like tracing filters)
+ * must not use these instructions unless ctx==skb
+ */
+int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
+			 int len)
+{
+	return -EFAULT;
+}
diff --git a/net/Kconfig b/net/Kconfig
index d92afe4204d9..a9582656856b 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -6,6 +6,7 @@ menuconfig NET
 	bool "Networking support"
 	select NLATTR
 	select GENERIC_NET_UTILS
+	select BPF
 	---help---
 	  Unless you really know what you are doing, you should say Y here.
 	  The reason is that some programs need kernel networking support even
-- 
1.7.9.5