Merge branch 'eBPF-based-device-cgroup-controller'

Roman Gushchin says:

====================
eBPF-based device cgroup controller

This patchset introduces an eBPF-based device controller for cgroup v2.

Patches (1) and (2) are a preparational work required to share some code
  with the existing device controller implementation.
Patch (3) is the main patch, which introduces a new bpf prog type
  and all necessary infrastructure.
Patch (4) moves cgroup_helpers.c/h to use them by patch (4).
Patch (5) implements an example of eBPF program which controls access
  to device files and corresponding userspace test.

v3:
  Renamed constants introduced by patch (3) to BPF_DEVCG_*

v2:
  Added patch (1).

v1:
  https://lkml.org/lkml/2017/11/1/363
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/bpf-cgroup.h

@@ -67,6 +67,9 @@ int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,
 				     struct bpf_sock_ops_kern *sock_ops,
 				     enum bpf_attach_type type);
 
+int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor,
+				      short access, enum bpf_attach_type type);
+
 /* Wrappers for __cgroup_bpf_run_filter_skb() guarded by cgroup_bpf_enabled. */
 #define BPF_CGROUP_RUN_PROG_INET_INGRESS(sk, skb)			      \
 ({									      \
@@ -112,6 +115,17 @@ int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,
 	}								       \
 	__ret;								       \
 })
+
+#define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access)	      \
+({									      \
+	int __ret = 0;							      \
+	if (cgroup_bpf_enabled)						      \
+		__ret = __cgroup_bpf_check_dev_permission(type, major, minor, \
+							  access,	      \
+							  BPF_CGROUP_DEVICE); \
+									      \
+	__ret;								      \
+})
 #else
 
 struct cgroup_bpf {};
@@ -122,6 +136,7 @@ static inline int cgroup_bpf_inherit(struct cgroup *cgrp) { return 0; }
 #define BPF_CGROUP_RUN_PROG_INET_EGRESS(sk,skb) ({ 0; })
 #define BPF_CGROUP_RUN_PROG_INET_SOCK(sk) ({ 0; })
 #define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops) ({ 0; })
+#define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type,major,minor,access) ({ 0; })
 
 #endif /* CONFIG_CGROUP_BPF */
 

include/linux/bpf_types.h

@@ -19,6 +19,9 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_KPROBE, kprobe)
 BPF_PROG_TYPE(BPF_PROG_TYPE_TRACEPOINT, tracepoint)
 BPF_PROG_TYPE(BPF_PROG_TYPE_PERF_EVENT, perf_event)
 #endif
+#ifdef CONFIG_CGROUP_BPF
+BPF_PROG_TYPE(BPF_PROG_TYPE_CGROUP_DEVICE, cg_dev)
+#endif
 
 BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)

include/linux/device_cgroup.h

@@ -1,17 +1,76 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/fs.h>
+#include <linux/bpf-cgroup.h>
+
+#define DEVCG_ACC_MKNOD 1
+#define DEVCG_ACC_READ  2
+#define DEVCG_ACC_WRITE 4
+#define DEVCG_ACC_MASK (DEVCG_ACC_MKNOD | DEVCG_ACC_READ | DEVCG_ACC_WRITE)
+
+#define DEVCG_DEV_BLOCK 1
+#define DEVCG_DEV_CHAR  2
+#define DEVCG_DEV_ALL   4  /* this represents all devices */
 
 #ifdef CONFIG_CGROUP_DEVICE
-extern int __devcgroup_inode_permission(struct inode *inode, int mask);
-extern int devcgroup_inode_mknod(int mode, dev_t dev);
+extern int __devcgroup_check_permission(short type, u32 major, u32 minor,
+					short access);
+#else
+static inline int __devcgroup_check_permission(short type, u32 major, u32 minor,
+					       short access)
+{ return 0; }
+#endif
+
+#if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
+static inline int devcgroup_check_permission(short type, u32 major, u32 minor,
+					     short access)
+{
+	int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
+
+	if (rc)
+		return -EPERM;
+
+	return __devcgroup_check_permission(type, major, minor, access);
+}
+
 static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 {
+	short type, access = 0;
+
 	if (likely(!inode->i_rdev))
 		return 0;
-	if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
+
+	if (S_ISBLK(inode->i_mode))
+		type = DEVCG_DEV_BLOCK;
+	else if (S_ISCHR(inode->i_mode))
+		type = DEVCG_DEV_CHAR;
+	else
+		return 0;
+
+	if (mask & MAY_WRITE)
+		access |= DEVCG_ACC_WRITE;
+	if (mask & MAY_READ)
+		access |= DEVCG_ACC_READ;
+
+	return devcgroup_check_permission(type, imajor(inode), iminor(inode),
+					  access);
+}
+
+static inline int devcgroup_inode_mknod(int mode, dev_t dev)
+{
+	short type;
+
+	if (!S_ISBLK(mode) && !S_ISCHR(mode))
 		return 0;
-	return __devcgroup_inode_permission(inode, mask);
+
+	if (S_ISBLK(mode))
+		type = DEVCG_DEV_BLOCK;
+	else
+		type = DEVCG_DEV_CHAR;
+
+	return devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
+					  DEVCG_ACC_MKNOD);
 }
+
 #else
 static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 { return 0; }

include/uapi/linux/bpf.h

@@ -132,6 +132,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_LWT_XMIT,
 	BPF_PROG_TYPE_SOCK_OPS,
 	BPF_PROG_TYPE_SK_SKB,
+	BPF_PROG_TYPE_CGROUP_DEVICE,
 };
 
 enum bpf_attach_type {
@@ -141,6 +142,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_SOCK_OPS,
 	BPF_SK_SKB_STREAM_PARSER,
 	BPF_SK_SKB_STREAM_VERDICT,
+	BPF_CGROUP_DEVICE,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -991,4 +993,17 @@ struct bpf_perf_event_value {
 	__u64 running;
 };
 
+#define BPF_DEVCG_ACC_MKNOD	(1ULL << 0)
+#define BPF_DEVCG_ACC_READ	(1ULL << 1)
+#define BPF_DEVCG_ACC_WRITE	(1ULL << 2)
+
+#define BPF_DEVCG_DEV_BLOCK	(1ULL << 0)
+#define BPF_DEVCG_DEV_CHAR	(1ULL << 1)
+
+struct bpf_cgroup_dev_ctx {
+	__u32 access_type; /* (access << 16) | type */
+	__u32 major;
+	__u32 minor;
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/cgroup.c

@@ -522,3 +522,70 @@ int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,
 	return ret == 1 ? 0 : -EPERM;
 }
 EXPORT_SYMBOL(__cgroup_bpf_run_filter_sock_ops);
+
+int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor,
+				      short access, enum bpf_attach_type type)
+{
+	struct cgroup *cgrp;
+	struct bpf_cgroup_dev_ctx ctx = {
+		.access_type = (access << 16) | dev_type,
+		.major = major,
+		.minor = minor,
+	};
+	int allow = 1;
+
+	rcu_read_lock();
+	cgrp = task_dfl_cgroup(current);
+	allow = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx,
+				   BPF_PROG_RUN);
+	rcu_read_unlock();
+
+	return !allow;
+}
+EXPORT_SYMBOL(__cgroup_bpf_check_dev_permission);
+
+static const struct bpf_func_proto *
+cgroup_dev_func_proto(enum bpf_func_id func_id)
+{
+	switch (func_id) {
+	case BPF_FUNC_map_lookup_elem:
+		return &bpf_map_lookup_elem_proto;
+	case BPF_FUNC_map_update_elem:
+		return &bpf_map_update_elem_proto;
+	case BPF_FUNC_map_delete_elem:
+		return &bpf_map_delete_elem_proto;
+	case BPF_FUNC_get_current_uid_gid:
+		return &bpf_get_current_uid_gid_proto;
+	case BPF_FUNC_trace_printk:
+		if (capable(CAP_SYS_ADMIN))
+			return bpf_get_trace_printk_proto();
+	default:
+		return NULL;
+	}
+}
+
+static bool cgroup_dev_is_valid_access(int off, int size,
+				       enum bpf_access_type type,
+				       struct bpf_insn_access_aux *info)
+{
+	if (type == BPF_WRITE)
+		return false;
+
+	if (off < 0 || off + size > sizeof(struct bpf_cgroup_dev_ctx))
+		return false;
+	/* The verifier guarantees that size > 0. */
+	if (off % size != 0)
+		return false;
+	if (size != sizeof(__u32))
+		return false;
+
+	return true;
+}
+
+const struct bpf_prog_ops cg_dev_prog_ops = {
+};
+
+const struct bpf_verifier_ops cg_dev_verifier_ops = {
+	.get_func_proto		= cgroup_dev_func_proto,
+	.is_valid_access	= cgroup_dev_is_valid_access,
+};

kernel/bpf/syscall.c

@@ -1326,6 +1326,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	case BPF_CGROUP_SOCK_OPS:
 		ptype = BPF_PROG_TYPE_SOCK_OPS;
 		break;
+	case BPF_CGROUP_DEVICE:
+		ptype = BPF_PROG_TYPE_CGROUP_DEVICE;
+		break;
 	case BPF_SK_SKB_STREAM_PARSER:
 	case BPF_SK_SKB_STREAM_VERDICT:
 		return sockmap_get_from_fd(attr, true);
@@ -1378,6 +1381,9 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 	case BPF_CGROUP_SOCK_OPS:
 		ptype = BPF_PROG_TYPE_SOCK_OPS;
 		break;
+	case BPF_CGROUP_DEVICE:
+		ptype = BPF_PROG_TYPE_CGROUP_DEVICE;
+		break;
 	case BPF_SK_SKB_STREAM_PARSER:
 	case BPF_SK_SKB_STREAM_VERDICT:
 		return sockmap_get_from_fd(attr, false);
@@ -1420,6 +1426,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
 	case BPF_CGROUP_INET_EGRESS:
 	case BPF_CGROUP_INET_SOCK_CREATE:
 	case BPF_CGROUP_SOCK_OPS:
+	case BPF_CGROUP_DEVICE:
 		break;
 	default:
 		return -EINVAL;

kernel/bpf/verifier.c

@@ -3124,6 +3124,7 @@ static int check_return_code(struct bpf_verifier_env *env)
 	case BPF_PROG_TYPE_CGROUP_SKB:
 	case BPF_PROG_TYPE_CGROUP_SOCK:
 	case BPF_PROG_TYPE_SOCK_OPS:
+	case BPF_PROG_TYPE_CGROUP_DEVICE:
 		break;
 	default:
 		return 0;

samples/bpf/Makefile

@@ -46,6 +46,7 @@ hostprogs-y += syscall_tp
 
 # Libbpf dependencies
 LIBBPF := ../../tools/lib/bpf/bpf.o
+CGROUP_HELPERS := ../../tools/testing/selftests/bpf/cgroup_helpers.o
 
 test_lru_dist-objs := test_lru_dist.o $(LIBBPF)
 sock_example-objs := sock_example.o $(LIBBPF)
@@ -69,13 +70,13 @@ map_perf_test-objs := bpf_load.o $(LIBBPF) map_perf_test_user.o
 test_overhead-objs := bpf_load.o $(LIBBPF) test_overhead_user.o
 test_cgrp2_array_pin-objs := $(LIBBPF) test_cgrp2_array_pin.o
 test_cgrp2_attach-objs := $(LIBBPF) test_cgrp2_attach.o
-test_cgrp2_attach2-objs := $(LIBBPF) test_cgrp2_attach2.o cgroup_helpers.o
+test_cgrp2_attach2-objs := $(LIBBPF) test_cgrp2_attach2.o $(CGROUP_HELPERS)
 test_cgrp2_sock-objs := $(LIBBPF) test_cgrp2_sock.o
 test_cgrp2_sock2-objs := bpf_load.o $(LIBBPF) test_cgrp2_sock2.o
 xdp1-objs := bpf_load.o $(LIBBPF) xdp1_user.o
 # reuse xdp1 source intentionally
 xdp2-objs := bpf_load.o $(LIBBPF) xdp1_user.o
-test_current_task_under_cgroup-objs := bpf_load.o $(LIBBPF) cgroup_helpers.o \
+test_current_task_under_cgroup-objs := bpf_load.o $(LIBBPF) $(CGROUP_HELPERS) \
 				       test_current_task_under_cgroup_user.o
 trace_event-objs := bpf_load.o $(LIBBPF) trace_event_user.o
 sampleip-objs := bpf_load.o $(LIBBPF) sampleip_user.o

security/device_cgroup.c

@@ -15,15 +15,6 @@
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>
 
-#define ACC_MKNOD 1
-#define ACC_READ  2
-#define ACC_WRITE 4
-#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
-
-#define DEV_BLOCK 1
-#define DEV_CHAR  2
-#define DEV_ALL   4  /* this represents all devices */
-
 static DEFINE_MUTEX(devcgroup_mutex);
 
 enum devcg_behavior {
@@ -246,21 +237,21 @@ static void set_access(char *acc, short access)
 {
 	int idx = 0;
 	memset(acc, 0, ACCLEN);
-	if (access & ACC_READ)
+	if (access & DEVCG_ACC_READ)
 		acc[idx++] = 'r';
-	if (access & ACC_WRITE)
+	if (access & DEVCG_ACC_WRITE)
 		acc[idx++] = 'w';
-	if (access & ACC_MKNOD)
+	if (access & DEVCG_ACC_MKNOD)
 		acc[idx++] = 'm';
 }
 
 static char type_to_char(short type)
 {
-	if (type == DEV_ALL)
+	if (type == DEVCG_DEV_ALL)
 		return 'a';
-	if (type == DEV_CHAR)
+	if (type == DEVCG_DEV_CHAR)
 		return 'c';
-	if (type == DEV_BLOCK)
+	if (type == DEVCG_DEV_BLOCK)
 		return 'b';
 	return 'X';
 }
@@ -287,10 +278,10 @@ static int devcgroup_seq_show(struct seq_file *m, void *v)
 	 * This way, the file remains as a "whitelist of devices"
 	 */
 	if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
-		set_access(acc, ACC_MASK);
+		set_access(acc, DEVCG_ACC_MASK);
 		set_majmin(maj, ~0);
 		set_majmin(min, ~0);
-		seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
+		seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 			   maj, min, acc);
 	} else {
 		list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
@@ -309,10 +300,10 @@ static int devcgroup_seq_show(struct seq_file *m, void *v)
 /**
  * match_exception	- iterates the exception list trying to find a complete match
  * @exceptions: list of exceptions
- * @type: device type (DEV_BLOCK or DEV_CHAR)
+ * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
  * @major: device file major number, ~0 to match all
  * @minor: device file minor number, ~0 to match all
- * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
+ * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
  *
  * It is considered a complete match if an exception is found that will
  * contain the entire range of provided parameters.
@@ -325,9 +316,9 @@ static bool match_exception(struct list_head *exceptions, short type,
 	struct dev_exception_item *ex;
 
 	list_for_each_entry_rcu(ex, exceptions, list) {
-		if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
+		if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 			continue;
-		if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
+		if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 			continue;
 		if (ex->major != ~0 && ex->major != major)
 			continue;
@@ -344,10 +335,10 @@ static bool match_exception(struct list_head *exceptions, short type,
 /**
  * match_exception_partial - iterates the exception list trying to find a partial match
  * @exceptions: list of exceptions
- * @type: device type (DEV_BLOCK or DEV_CHAR)
+ * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
  * @major: device file major number, ~0 to match all
  * @minor: device file minor number, ~0 to match all
- * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
+ * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
  *
  * It is considered a partial match if an exception's range is found to
  * contain *any* of the devices specified by provided parameters. This is
@@ -362,9 +353,9 @@ static bool match_exception_partial(struct list_head *exceptions, short type,
 	struct dev_exception_item *ex;
 
 	list_for_each_entry_rcu(ex, exceptions, list) {
-		if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
+		if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 			continue;
-		if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
+		if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 			continue;
 		/*
 		 * We must be sure that both the exception and the provided
@@ -647,10 +638,10 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 		}
 		return 0;
 	case 'b':
-		ex.type = DEV_BLOCK;
+		ex.type = DEVCG_DEV_BLOCK;
 		break;
 	case 'c':
-		ex.type = DEV_CHAR;
+		ex.type = DEVCG_DEV_CHAR;
 		break;
 	default:
 		return -EINVAL;
@@ -703,13 +694,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 	for (b++, count = 0; count < 3; count++, b++) {
 		switch (*b) {
 		case 'r':
-			ex.access |= ACC_READ;
+			ex.access |= DEVCG_ACC_READ;
 			break;
 		case 'w':
-			ex.access |= ACC_WRITE;
+			ex.access |= DEVCG_ACC_WRITE;
 			break;
 		case 'm':
-			ex.access |= ACC_MKNOD;
+			ex.access |= DEVCG_ACC_MKNOD;
 			break;
 		case '\n':
 		case '\0':
@@ -806,12 +797,12 @@ struct cgroup_subsys devices_cgrp_subsys = {
  * @type: device type
  * @major: device major number
  * @minor: device minor number
- * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
+ * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
  *
  * returns 0 on success, -EPERM case the operation is not permitted
  */
-static int __devcgroup_check_permission(short type, u32 major, u32 minor,
-				        short access)
+int __devcgroup_check_permission(short type, u32 major, u32 minor,
+				 short access)
 {
 	struct dev_cgroup *dev_cgroup;
 	bool rc;
@@ -833,37 +824,3 @@ static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 
 	return 0;
 }
-
-int __devcgroup_inode_permission(struct inode *inode, int mask)
-{
-	short type, access = 0;
-
-	if (S_ISBLK(inode->i_mode))
-		type = DEV_BLOCK;
-	if (S_ISCHR(inode->i_mode))
-		type = DEV_CHAR;
-	if (mask & MAY_WRITE)
-		access |= ACC_WRITE;
-	if (mask & MAY_READ)
-		access |= ACC_READ;
-
-	return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
-			access);
-}
-
-int devcgroup_inode_mknod(int mode, dev_t dev)
-{
-	short type;
-
-	if (!S_ISBLK(mode) && !S_ISCHR(mode))
-		return 0;
-
-	if (S_ISBLK(mode))
-		type = DEV_BLOCK;
-	else
-		type = DEV_CHAR;
-
-	return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
-			ACC_MKNOD);
-
-}

tools/include/uapi/linux/bpf.h

@@ -131,6 +131,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_LWT_XMIT,
 	BPF_PROG_TYPE_SOCK_OPS,
 	BPF_PROG_TYPE_SK_SKB,
+	BPF_PROG_TYPE_CGROUP_DEVICE,
 };
 
 enum bpf_attach_type {
@@ -140,6 +141,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_SOCK_OPS,
 	BPF_SK_SKB_STREAM_PARSER,
 	BPF_SK_SKB_STREAM_VERDICT,
+	BPF_CGROUP_DEVICE,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -990,4 +992,17 @@ struct bpf_perf_event_value {
 	__u64 running;
 };
 
+#define BPF_DEVCG_ACC_MKNOD	(1ULL << 0)
+#define BPF_DEVCG_ACC_READ	(1ULL << 1)
+#define BPF_DEVCG_ACC_WRITE	(1ULL << 2)
+
+#define BPF_DEVCG_DEV_BLOCK	(1ULL << 0)
+#define BPF_DEVCG_DEV_CHAR	(1ULL << 1)
+
+struct bpf_cgroup_dev_ctx {
+	__u32 access_type; /* (access << 16) | type */
+	__u32 major;
+	__u32 minor;
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */

tools/testing/selftests/bpf/Makefile

@@ -13,17 +13,17 @@ CFLAGS += -Wall -O2 -I$(APIDIR) -I$(LIBDIR) -I$(GENDIR) $(GENFLAGS) -I../../../i
 LDLIBS += -lcap -lelf
 
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test_progs \
-	test_align test_verifier_log
+	test_align test_verifier_log test_dev_cgroup
 
 TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test_obj_id.o \
 	test_pkt_md_access.o test_xdp_redirect.o test_xdp_meta.o sockmap_parse_prog.o     \
-	sockmap_verdict_prog.o
+	sockmap_verdict_prog.o dev_cgroup.o
 
 TEST_PROGS := test_kmod.sh test_xdp_redirect.sh test_xdp_meta.sh
 
 include ../lib.mk
 
-BPFOBJ := $(OUTPUT)/libbpf.a
+BPFOBJ := $(OUTPUT)/libbpf.a $(OUTPUT)/cgroup_helpers.c
 
 $(TEST_GEN_PROGS): $(BPFOBJ)
 

tools/testing/selftests/bpf/dev_cgroup.c

@@ -0,0 +1,60 @@
+/* Copyright (c) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+
+#include <linux/bpf.h>
+#include <linux/version.h>
+#include "bpf_helpers.h"
+
+SEC("cgroup/dev")
+int bpf_prog1(struct bpf_cgroup_dev_ctx *ctx)
+{
+	short type = ctx->access_type & 0xFFFF;
+#ifdef DEBUG
+	short access = ctx->access_type >> 16;
+	char fmt[] = "  %d:%d    \n";
+
+	switch (type) {
+	case BPF_DEVCG_DEV_BLOCK:
+		fmt[0] = 'b';
+		break;
+	case BPF_DEVCG_DEV_CHAR:
+		fmt[0] = 'c';
+		break;
+	default:
+		fmt[0] = '?';
+		break;
+	}
+
+	if (access & BPF_DEVCG_ACC_READ)
+		fmt[8] = 'r';
+
+	if (access & BPF_DEVCG_ACC_WRITE)
+		fmt[9] = 'w';
+
+	if (access & BPF_DEVCG_ACC_MKNOD)
+		fmt[10] = 'm';
+
+	bpf_trace_printk(fmt, sizeof(fmt), ctx->major, ctx->minor);
+#endif
+
+	/* Allow access to /dev/zero and /dev/random.
+	 * Forbid everything else.
+	 */
+	if (ctx->major != 1 || type != BPF_DEVCG_DEV_CHAR)
+		return 0;
+
+	switch (ctx->minor) {
+	case 5: /* 1:5 /dev/zero */
+	case 9: /* 1:9 /dev/urandom */
+		return 1;
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+__u32 _version SEC("version") = LINUX_VERSION_CODE;

tools/testing/selftests/bpf/test_dev_cgroup.c

@@ -0,0 +1,93 @@
+/* Copyright (c) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+
+#include <linux/bpf.h>
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+
+#include "cgroup_helpers.h"
+
+#define DEV_CGROUP_PROG "./dev_cgroup.o"
+
+#define TEST_CGROUP "test-bpf-based-device-cgroup/"
+
+int main(int argc, char **argv)
+{
+	struct bpf_object *obj;
+	int error = EXIT_FAILURE;
+	int prog_fd, cgroup_fd;
+	__u32 prog_cnt;
+
+	if (bpf_prog_load(DEV_CGROUP_PROG, BPF_PROG_TYPE_CGROUP_DEVICE,
+			  &obj, &prog_fd)) {
+		printf("Failed to load DEV_CGROUP program\n");
+		goto err;
+	}
+
+	if (setup_cgroup_environment()) {
+		printf("Failed to load DEV_CGROUP program\n");
+		goto err;
+	}
+
+	/* Create a cgroup, get fd, and join it */
+	cgroup_fd = create_and_get_cgroup(TEST_CGROUP);
+	if (!cgroup_fd) {
+		printf("Failed to create test cgroup\n");
+		goto err;
+	}
+
+	if (join_cgroup(TEST_CGROUP)) {
+		printf("Failed to join cgroup\n");
+		goto err;
+	}
+
+	/* Attach bpf program */
+	if (bpf_prog_attach(prog_fd, cgroup_fd, BPF_CGROUP_DEVICE, 0)) {
+		printf("Failed to attach DEV_CGROUP program");
+		goto err;
+	}
+
+	if (bpf_prog_query(cgroup_fd, BPF_CGROUP_DEVICE, 0, NULL, NULL,
+			   &prog_cnt)) {
+		printf("Failed to query attached programs");
+		goto err;
+	}
+
+	/* All operations with /dev/zero and and /dev/urandom are allowed,
+	 * everything else is forbidden.
+	 */
+	assert(system("rm -f /tmp/test_dev_cgroup_null") == 0);
+	assert(system("mknod /tmp/test_dev_cgroup_null c 1 3"));
+	assert(system("rm -f /tmp/test_dev_cgroup_null") == 0);
+
+	/* /dev/zero is whitelisted */
+	assert(system("rm -f /tmp/test_dev_cgroup_zero") == 0);
+	assert(system("mknod /tmp/test_dev_cgroup_zero c 1 5") == 0);
+	assert(system("rm -f /tmp/test_dev_cgroup_zero") == 0);
+
+	assert(system("dd if=/dev/urandom of=/dev/zero count=64") == 0);
+
+	/* src is allowed, target is forbidden */
+	assert(system("dd if=/dev/urandom of=/dev/full count=64"));
+
+	/* src is forbidden, target is allowed */
+	assert(system("dd if=/dev/random of=/dev/zero count=64"));
+
+	error = 0;
+	printf("test_dev_cgroup:PASS\n");
+
+err:
+	cleanup_cgroup_environment();
+
+	return error;
+}