[PATCH 2/3] security: bpf: Add eBPF LSM hooks and security field to eBPF map

On Thu, Aug 31, 2017 at 7:05 PM, Alexei Starovoitov

...

@@ -410,6 +418,10 @@ static int map_lookup_elem(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_read(map);
+ if (err)
+ return -EACCES;
+
key = memdup_user(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
@@ -490,6 +502,10 @@ static int map_update_elem(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_modify(map);

I don't feel these extra hooks are really thought through.
With such hook you'll disallow map_update for given map. That's it.
The key/values etc won't be used in such security decision.
In such case you don't need such hooks in update/lookup at all.
Only in map_creation and object_get calls where FD can be received.
Do permissions checks in open() and allow read/write() if FD is valid.
Same here. Do permission checks in prog_load/map_create/obj_pin/get
and that will be enough to jail bpf subsystem.
bpf cmds that need to be fast (like lookup and update) should not
have security hooks.

I do think we want to distinguish between read/write (or read/modify)
for these objects. Essentially, we want to implement the example
described in patch 0/3 where eBPF objects can be passed to less
privileged processes which can read, but not modify the map. What
would be the best way to do this? Add a mode field to the bpf_map
struct?

Chenbo Feng

2017-08-31 20:56:35 UTC

From: Chenbo Feng <***@google.com>

Introduce 5 new selinux checks for eBPF object related operations. The
check is based on the ownership information of eBPF maps and the
capability of creating eBPF object.

Signed-off-by: Chenbo Feng <***@google.com>
---
security/selinux/hooks.c | 54 +++++++++++++++++++++++++++++++++++++
security/selinux/include/classmap.h | 2 ++
security/selinux/include/objsec.h | 4 +++
3 files changed, 60 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 33fd061305c4..39ad7d9f335d 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -85,6 +85,7 @@
#include <linux/export.h>
#include <linux/msg.h>
#include <linux/shm.h>
+#include <linux/bpf.h>

#include "avc.h"
#include "objsec.h"
@@ -6245,6 +6246,52 @@ static void selinux_ib_free_security(void *ib_sec)
}
#endif

+#ifdef CONFIG_BPF_SYSCALL
+static int selinux_bpf_map_create(void)
+{
+ u32 sid = current_sid();
+
+ return avc_has_perm(sid, sid, SECCLASS_BPF, BPF__MAP_CREATE, NULL);
+}
+
+static int selinux_bpf_map_modify(struct bpf_map *map)
+{
+ struct bpf_security_struct *bpfsec = map->security;
+
+ return avc_has_perm(current_sid(), bpfsec->sid, SECCLASS_BPF,
+ BPF__MAP_MODIFY, NULL);
+}
+
+static int selinux_bpf_map_read(struct bpf_map *map)
+{
+ struct bpf_security_struct *bpfsec = map->security;
+
+ return avc_has_perm(current_sid(), bpfsec->sid, SECCLASS_BPF,
+ BPF__MAP_READ, NULL);
+}
+
+static int selinux_bpf_prog_load(void)
+{
+ u32 sid = current_sid();
+
+ return avc_has_perm(sid, sid, SECCLASS_BPF, BPF__PROG_LOAD, NULL);
+}
+
+static int selinux_bpf_post_create(struct bpf_map *map)
+{
+ struct bpf_security_struct *bpfsec;
+
+ bpfsec = kzalloc(sizeof(*bpfsec), GFP_KERNEL);
+ if (!bpfsec)
+ return -ENOMEM;
+
+ bpfsec->sid = current_sid();
+ map->security = bpfsec;
+
+ return 0;
+}
+#endif
+
static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(binder_set_context_mgr, selinux_binder_set_context_mgr),
LSM_HOOK_INIT(binder_transaction, selinux_binder_transaction),
@@ -6465,6 +6512,13 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(audit_rule_match, selinux_audit_rule_match),
LSM_HOOK_INIT(audit_rule_free, selinux_audit_rule_free),
#endif
+#ifdef CONFIG_BPF_SYSCALL
+ LSM_HOOK_INIT(bpf_map_create, selinux_bpf_map_create),
+ LSM_HOOK_INIT(bpf_map_modify, selinux_bpf_map_modify),
+ LSM_HOOK_INIT(bpf_map_read, selinux_bpf_map_read),
+ LSM_HOOK_INIT(bpf_prog_load, selinux_bpf_prog_load),
+ LSM_HOOK_INIT(bpf_post_create, selinux_bpf_post_create),
+#endif
};

static __init int selinux_init(void)
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index b9fe3434b036..83c880fb17b4 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -235,6 +235,8 @@ struct security_class_mapping secclass_map[] = {
{ "access", NULL } },
{ "infiniband_endport",
{ "manage_subnet", NULL } },
+ { "bpf",
+ {"map_create", "map_modify", "map_read", "prog_load" } },
{ NULL }
};

diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
index 6ebc61e370ff..ba564f662b0d 100644
--- a/security/selinux/include/objsec.h
+++ b/security/selinux/include/objsec.h
@@ -150,6 +150,10 @@ struct pkey_security_struct {
u32 sid; /* SID of pkey */
};

+struct bpf_security_struct {
+ u32 sid; /*SID of bpf obj creater*/
+};
+
extern unsigned int selinux_checkreqprot;

#endif /* _SELINUX_OBJSEC_H_ */

--
2.14.1.581.gf28d330327-goog

Chenbo Feng

2017-08-31 20:56:33 UTC

From: Chenbo Feng <***@google.com>

Introduce 5 LSM hooks to provide finer granularity controls on eBPF
related operations including create eBPF maps, modify and read eBPF maps
content and load eBPF programs to the kernel. Hooks use the new security
pointer inside the eBPF map struct to store the owner's security
information and the different security modules can perform different
checks based on the information stored inside the security field.

Signed-off-by: Chenbo Feng <***@google.com>
---
include/linux/lsm_hooks.h | 41 +++++++++++++++++++++++++++++++++++++++++
include/linux/security.h | 36 ++++++++++++++++++++++++++++++++++++
security/security.c | 28 ++++++++++++++++++++++++++++
3 files changed, 105 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ce02f76a6188..3aaf9a08a983 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1353,6 +1353,32 @@
* @inode we wish to get the security context of.
* @ctx is a pointer in which to place the allocated security context.
* @ctxlen points to the place to put the length of @ctx.
+ *
+ * Security hooks for using the eBPF maps and programs functionalities through
+ * eBPF syscalls.
+ *
+ * @bpf_map_create:
+ * Check permissions prior to creating a new bpf map.
+ * Return 0 if the permission is granted.
+ *
+ * @bpf_map_modify:
+ * Check permission prior to insert, update and delete map content.
+ * @map pointer to the struct bpf_map that contains map information.
+ * Return 0 if the permission is granted.
+ *
+ * @bpf_map_read:
+ * Check permission prior to read a bpf map content.
+ * @map pointer to the struct bpf_map that contains map information.
+ * Return 0 if the permission is granted.
+ *
+ * @bpf_prog_load:
+ * Check permission prior to load eBPF program.
+ * Return 0 if the permission is granted.
+ *
+ * @bpf_post_create:
+ * Initialize the bpf object security field inside struct bpf_maps and
+ * it is used for future security checks.
+ *
*/
union security_list_options {
int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1685,6 +1711,14 @@ union security_list_options {
struct audit_context *actx);
void (*audit_rule_free)(void *lsmrule);
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+ int (*bpf_map_create)(void);
+ int (*bpf_map_read)(struct bpf_map *map);
+ int (*bpf_map_modify)(struct bpf_map *map);
+ int (*bpf_prog_load)(void);
+ int (*bpf_post_create)(struct bpf_map *map);
+#endif /* CONFIG_BPF_SYSCALL */
};

struct security_hook_heads {
@@ -1905,6 +1939,13 @@ struct security_hook_heads {
struct list_head audit_rule_match;
struct list_head audit_rule_free;
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_BPF_SYSCALL
+ struct list_head bpf_map_create;
+ struct list_head bpf_map_read;
+ struct list_head bpf_map_modify;
+ struct list_head bpf_prog_load;
+ struct list_head bpf_post_create;
+#endif /* CONFIG_BPF_SYSCALL */
} __randomize_layout;

/*
diff --git a/include/linux/security.h b/include/linux/security.h
index 458e24bea2d4..0656a4f74d14 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -31,6 +31,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/bpf.h>

struct linux_binprm;
struct cred;
@@ -1735,6 +1736,41 @@ static inline void securityfs_remove(struct dentry *dentry)

#endif

+#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_SECURITY
+int security_map_create(void);
+int security_map_modify(struct bpf_map *map);
+int security_map_read(struct bpf_map *map);
+int security_prog_load(void);
+int security_post_create(struct bpf_map *map);
+#else
+static inline int security_map_create(void)
+{
+ return 0;
+}
+
+static inline int security_map_read(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_map_modify(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_prog_load(void)
+{
+ return 0;
+}
+
+static inline int security_post_create(struct bpf_map *map)
+{
+ return 0;
+}
+#endif /* CONFIG_SECURITY */
+#endif /* CONFIG_BPF_SYSCALL */
+
#ifdef CONFIG_SECURITY

static inline char *alloc_secdata(void)
diff --git a/security/security.c b/security/security.c
index 55b5997e4b72..02272f93a89e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -12,6 +12,7 @@
* (at your option) any later version.
*/

+#include <linux/bpf.h>
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/module.h>
@@ -1708,3 +1709,30 @@ int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule,
actx);
}
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+int security_map_create(void)
+{
+ return call_int_hook(bpf_map_create, 0);
+}
+
+int security_map_modify(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_modify, 0, map);
+}
+
+int security_map_read(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_read, 0, map);
+}
+
+int security_prog_load(void)
+{
+ return call_int_hook(bpf_prog_load, 0);
+}
+
+int security_post_create(struct bpf_map *map)
+{
+ return call_int_hook(bpf_post_create, 0, map);
+}
+#endif /* CONFIG_BPF_SYSCALL */

--
2.14.1.581.gf28d330327-goog

Stephen Smalley

2017-09-01 12:50:23 UTC

Post by Chenbo Feng
Introduce 5 LSM hooks to provide finer granularity controls on eBPF
related operations including create eBPF maps, modify and read eBPF maps
content and load eBPF programs to the kernel. Hooks use the new security
pointer inside the eBPF map struct to store the owner's security
information and the different security modules can perform different
checks based on the information stored inside the security field.
---
include/linux/lsm_hooks.h | 41
+++++++++++++++++++++++++++++++++++++++++
include/linux/security.h | 36 ++++++++++++++++++++++++++++++++++++
security/security.c | 28 ++++++++++++++++++++++++++++
3 files changed, 105 insertions(+)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ce02f76a6188..3aaf9a08a983 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1353,6 +1353,32 @@
context.
+ *
+ * Security hooks for using the eBPF maps and programs
functionalities through
+ * eBPF syscalls.
+ *
+ * Check permissions prior to creating a new bpf map.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to insert, update and delete map
content.
information.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to read a bpf map content.
information.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to load eBPF program.
+ * Return 0 if the permission is granted.
+ *
+ * Initialize the bpf object security field inside struct
bpf_maps and
+ * it is used for future security checks.
+ *
*/
union security_list_options {
int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1685,6 +1711,14 @@ union security_list_options {
struct audit_context *actx);
void (*audit_rule_free)(void *lsmrule);
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+ int (*bpf_map_create)(void);
+ int (*bpf_map_read)(struct bpf_map *map);
+ int (*bpf_map_modify)(struct bpf_map *map);
+ int (*bpf_prog_load)(void);
+ int (*bpf_post_create)(struct bpf_map *map);
+#endif /* CONFIG_BPF_SYSCALL */
};

struct security_hook_heads {
@@ -1905,6 +1939,13 @@ struct security_hook_heads {
struct list_head audit_rule_match;
struct list_head audit_rule_free;
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_BPF_SYSCALL
+ struct list_head bpf_map_create;
+ struct list_head bpf_map_read;
+ struct list_head bpf_map_modify;
+ struct list_head bpf_prog_load;
+ struct list_head bpf_post_create;
+#endif /* CONFIG_BPF_SYSCALL */
} __randomize_layout;

/*
diff --git a/include/linux/security.h b/include/linux/security.h
index 458e24bea2d4..0656a4f74d14 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -31,6 +31,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/bpf.h>

struct linux_binprm;
struct cred;
@@ -1735,6 +1736,41 @@ static inline void securityfs_remove(struct dentry *dentry)

#endif

+#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_SECURITY
+int security_map_create(void);
+int security_map_modify(struct bpf_map *map);
+int security_map_read(struct bpf_map *map);
+int security_prog_load(void);
+int security_post_create(struct bpf_map *map);
+#else
+static inline int security_map_create(void)
+{
+ return 0;
+}
+
+static inline int security_map_read(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_map_modify(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_prog_load(void)
+{
+ return 0;
+}
+
+static inline int security_post_create(struct bpf_map *map)
+{
+ return 0;
+}
+#endif /* CONFIG_SECURITY */
+#endif /* CONFIG_BPF_SYSCALL */

These should be named consistently with the ones in lsm_hooks.h and
should unambiguously indicate that these are hooks for bpf
objects/operations, i.e. security_bpf_map_create(),
security_bpf_map_read(), etc.

Do you need this level of granularity?

Could you coalesce the map_create() and post_map_create() hooks into
one hook and just unwind the create in that case?

Why do you label bpf maps but not bpf progs? Should we be controlling
the ability to attach/detach a bpf prog (partly controlled by
CAP_NET_ADMIN, but also somewhat broad in scope and doesn't allow
control based on who created the prog)?

Should there be a top-level security_bpf_use() hook and permission
check that limits ability to use bpf() at all?

Post by Chenbo Feng
+
#ifdef CONFIG_SECURITY

static inline char *alloc_secdata(void)
diff --git a/security/security.c b/security/security.c
index 55b5997e4b72..02272f93a89e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -12,6 +12,7 @@
* (at your option) any later version.
*/

+#include <linux/bpf.h>
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/module.h>
@@ -1708,3 +1709,30 @@ int security_audit_rule_match(u32 secid, u32
field, u32 op, void *lsmrule,
actx);
}
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+int security_map_create(void)
+{
+ return call_int_hook(bpf_map_create, 0);
+}
+
+int security_map_modify(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_modify, 0, map);
+}
+
+int security_map_read(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_read, 0, map);
+}
+
+int security_prog_load(void)
+{
+ return call_int_hook(bpf_prog_load, 0);
+}
+
+int security_post_create(struct bpf_map *map)
+{
+ return call_int_hook(bpf_post_create, 0, map);
+}
+#endif /* CONFIG_BPF_SYSCALL */

Chenbo Feng via Selinux

2017-09-05 22:24:22 UTC

Post by Chenbo Feng
Introduce 5 LSM hooks to provide finer granularity controls on eBPF
related operations including create eBPF maps, modify and read eBPF maps
content and load eBPF programs to the kernel. Hooks use the new security
pointer inside the eBPF map struct to store the owner's security
information and the different security modules can perform different
checks based on the information stored inside the security field.
---
include/linux/lsm_hooks.h | 41
+++++++++++++++++++++++++++++++++++++++++
include/linux/security.h | 36 ++++++++++++++++++++++++++++++++++++
security/security.c | 28 ++++++++++++++++++++++++++++
3 files changed, 105 insertions(+)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ce02f76a6188..3aaf9a08a983 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1353,6 +1353,32 @@
context.
+ *
+ * Security hooks for using the eBPF maps and programs
functionalities through
+ * eBPF syscalls.
+ *
+ * Check permissions prior to creating a new bpf map.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to insert, update and delete map
content.
information.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to read a bpf map content.
information.
+ * Return 0 if the permission is granted.
+ *
+ * Check permission prior to load eBPF program.
+ * Return 0 if the permission is granted.
+ *
+ * Initialize the bpf object security field inside struct
bpf_maps and
+ * it is used for future security checks.
+ *
*/
union security_list_options {
int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1685,6 +1711,14 @@ union security_list_options {
struct audit_context *actx);
void (*audit_rule_free)(void *lsmrule);
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+ int (*bpf_map_create)(void);
+ int (*bpf_map_read)(struct bpf_map *map);
+ int (*bpf_map_modify)(struct bpf_map *map);
+ int (*bpf_prog_load)(void);
+ int (*bpf_post_create)(struct bpf_map *map);
+#endif /* CONFIG_BPF_SYSCALL */
};
struct security_hook_heads {
@@ -1905,6 +1939,13 @@ struct security_hook_heads {
struct list_head audit_rule_match;
struct list_head audit_rule_free;
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_BPF_SYSCALL
+ struct list_head bpf_map_create;
+ struct list_head bpf_map_read;
+ struct list_head bpf_map_modify;
+ struct list_head bpf_prog_load;
+ struct list_head bpf_post_create;
+#endif /* CONFIG_BPF_SYSCALL */
} __randomize_layout;
/*
diff --git a/include/linux/security.h b/include/linux/security.h
index 458e24bea2d4..0656a4f74d14 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -31,6 +31,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/bpf.h>
struct linux_binprm;
struct cred;
@@ -1735,6 +1736,41 @@ static inline void securityfs_remove(struct dentry *dentry)
#endif
+#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_SECURITY
+int security_map_create(void);
+int security_map_modify(struct bpf_map *map);
+int security_map_read(struct bpf_map *map);
+int security_prog_load(void);
+int security_post_create(struct bpf_map *map);
+#else
+static inline int security_map_create(void)
+{
+ return 0;
+}
+
+static inline int security_map_read(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_map_modify(struct bpf_map *map)
+{
+ return 0;
+}
+
+static inline int security_prog_load(void)
+{
+ return 0;
+}
+
+static inline int security_post_create(struct bpf_map *map)
+{
+ return 0;
+}
+#endif /* CONFIG_SECURITY */
+#endif /* CONFIG_BPF_SYSCALL */

Thanks for pointing out, will fix this.

Post by Stephen Smalley
Do you need this level of granularity?

The cover letter of this patch series described a possible use cases of
these lsm hooks and this level of granularity would be ideal to reach that
goal. We can also implement two hooks such as bpf_obj_create and
bpf_obj_use to restrict the creation and using when get the bpf fd from
kernel. But that will be less powerful and flexible.

Post by Stephen Smalley
Could you coalesce the map_create() and post_map_create() hooks into
one hook and just unwind the create in that case?

Okay, I will take a look on how to fix this.

Post by Stephen Smalley
Why do you label bpf maps but not bpf progs? Should we be controlling
the ability to attach/detach a bpf prog (partly controlled by
CAP_NET_ADMIN, but also somewhat broad in scope and doesn't allow
control based on who created the prog)?
Should there be a top-level security_bpf_use() hook and permission
check that limits ability to use bpf() at all?

This could be useful but having additional lsm hooks check when reading
and write to eBPF maps may cause performance issue. Instead maybe we
could have a hook for creating eBPF object and retrieve object fd to restrict
the access.

Post by Chenbo Feng
+
#ifdef CONFIG_SECURITY
static inline char *alloc_secdata(void)
diff --git a/security/security.c b/security/security.c
index 55b5997e4b72..02272f93a89e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -12,6 +12,7 @@
* (at your option) any later version.
*/
+#include <linux/bpf.h>
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/module.h>
@@ -1708,3 +1709,30 @@ int security_audit_rule_match(u32 secid, u32
field, u32 op, void *lsmrule,
actx);
}
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+int security_map_create(void)
+{
+ return call_int_hook(bpf_map_create, 0);
+}
+
+int security_map_modify(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_modify, 0, map);
+}
+
+int security_map_read(struct bpf_map *map)
+{
+ return call_int_hook(bpf_map_read, 0, map);
+}
+
+int security_prog_load(void)
+{
+ return call_int_hook(bpf_prog_load, 0);
+}
+
+int security_post_create(struct bpf_map *map)
+{
+ return call_int_hook(bpf_post_create, 0, map);
+}
+#endif /* CONFIG_BPF_SYSCALL */

Stephen Smalley

2017-09-07 12:32:19 UTC

Post by Chenbo Feng via Selinux

Post by Chenbo Feng via Selinux

Post by Chenbo Feng
Introduce 5 LSM hooks to provide finer granularity controls on eBPF
related operations including create eBPF maps, modify and read
eBPF
maps
content and load eBPF programs to the kernel. Hooks use the new security
pointer inside the eBPF map struct to store the owner's security
information and the different security modules can perform
different
checks based on the information stored inside the security field.
---
include/linux/lsm_hooks.h | 41
+++++++++++++++++++++++++++++++++++++++++
include/linux/security.h  | 36
++++++++++++++++++++++++++++++++++++
security/security.c       | 28 ++++++++++++++++++++++++++++
3 files changed, 105 insertions(+)
diff --git a/include/linux/lsm_hooks.h
b/include/linux/lsm_hooks.h
index ce02f76a6188..3aaf9a08a983 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1353,6 +1353,32 @@
context.
+ *
+ * Security hooks for using the eBPF maps and programs
functionalities through
+ * eBPF syscalls.
+ *
+ *   Check permissions prior to creating a new bpf map.
+ *   Return 0 if the permission is granted.
+ *
+ *   Check permission prior to insert, update and delete map
content.
information.
+ *   Return 0 if the permission is granted.
+ *
+ *   Check permission prior to read a bpf map content.
information.
+ *   Return 0 if the permission is granted.
+ *
+ *   Check permission prior to load eBPF program.
+ *   Return 0 if the permission is granted.
+ *
+ *   Initialize the bpf object security field inside struct
bpf_maps and
+ *   it is used for future security checks.
+ *
*/
union security_list_options {
      int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1685,6 +1711,14 @@ union security_list_options {
                              struct audit_context *actx);
      void (*audit_rule_free)(void *lsmrule);
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+     int (*bpf_map_create)(void);
+     int (*bpf_map_read)(struct bpf_map *map);
+     int (*bpf_map_modify)(struct bpf_map *map);
+     int (*bpf_prog_load)(void);
+     int (*bpf_post_create)(struct bpf_map *map);
+#endif /* CONFIG_BPF_SYSCALL */
};
struct security_hook_heads {
@@ -1905,6 +1939,13 @@ struct security_hook_heads {
      struct list_head audit_rule_match;
      struct list_head audit_rule_free;
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_BPF_SYSCALL
+     struct list_head bpf_map_create;
+     struct list_head bpf_map_read;
+     struct list_head bpf_map_modify;
+     struct list_head bpf_prog_load;
+     struct list_head bpf_post_create;
+#endif /* CONFIG_BPF_SYSCALL */
} __randomize_layout;
/*
diff --git a/include/linux/security.h b/include/linux/security.h
index 458e24bea2d4..0656a4f74d14 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -31,6 +31,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/fs.h>
+#include <linux/bpf.h>
struct linux_binprm;
struct cred;
@@ -1735,6 +1736,41 @@ static inline void
securityfs_remove(struct
dentry *dentry)
#endif
+#ifdef CONFIG_BPF_SYSCALL
+#ifdef CONFIG_SECURITY
+int security_map_create(void);
+int security_map_modify(struct bpf_map *map);
+int security_map_read(struct bpf_map *map);
+int security_prog_load(void);
+int security_post_create(struct bpf_map *map);
+#else
+static inline int security_map_create(void)
+{
+     return 0;
+}
+
+static inline int security_map_read(struct bpf_map *map)
+{
+     return 0;
+}
+
+static inline int security_map_modify(struct bpf_map *map)
+{
+     return 0;
+}
+
+static inline int security_prog_load(void)
+{
+     return 0;
+}
+
+static inline int security_post_create(struct bpf_map *map)
+{
+     return 0;
+}
+#endif /* CONFIG_SECURITY */
+#endif /* CONFIG_BPF_SYSCALL */

Thanks for pointing out, will fix this.

Post by Stephen Smalley
Do you need this level of granularity?

Post by Stephen Smalley
Could you coalesce the map_create() and post_map_create() hooks into
one hook and just unwind the create in that case?

Okay, I will take a look on how to fix this.

Also, what you called security_post_create() would normally be called
something like security_bpf_alloc_security(), and would have a
corresponding security_bpf_free_security() hook too. However, whether
or not you still need this security field and hook at all is unclear to
me, given the direction the discussion has gone.

Post by Stephen Smalley
Why do you label bpf maps but not bpf progs? Should we be
controlling
the ability to attach/detach a bpf prog (partly controlled by
CAP_NET_ADMIN, but also somewhat broad in scope and doesn't allow
control based on who created the prog)?
Should there be a top-level security_bpf_use() hook and permission
check that limits ability to use bpf() at all?

Post by Chenbo Feng
+
#ifdef CONFIG_SECURITY
static inline char *alloc_secdata(void)
diff --git a/security/security.c b/security/security.c
index 55b5997e4b72..02272f93a89e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -12,6 +12,7 @@
*   (at your option) any later version.
*/
+#include <linux/bpf.h>
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/module.h>
@@ -1708,3 +1709,30 @@ int security_audit_rule_match(u32 secid, u32
field, u32 op, void *lsmrule,
                              actx);
}
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_BPF_SYSCALL
+int security_map_create(void)
+{
+     return call_int_hook(bpf_map_create, 0);
+}
+
+int security_map_modify(struct bpf_map *map)
+{
+     return call_int_hook(bpf_map_modify, 0, map);
+}
+
+int security_map_read(struct bpf_map *map)
+{
+     return call_int_hook(bpf_map_read, 0, map);
+}
+
+int security_prog_load(void)
+{
+     return call_int_hook(bpf_prog_load, 0);
+}
+
+int security_post_create(struct bpf_map *map)
+{
+     return call_int_hook(bpf_post_create, 0, map);
+}
+#endif /* CONFIG_BPF_SYSCALL */

Chenbo Feng via Selinux

2017-08-31 22:17:40 UTC

Post by Mimi Zohar

Any reason not to just return err?
Mimi

Nope... return err might be better. I will fix this in next version.

Thanks
Chenbo

Post by Mimi Zohar

Daniel Borkmann

2017-08-31 22:38:40 UTC

Against which tree is this by the way, net-next? There are
changes here which require a rebase of your set.

---
include/linux/bpf.h | 3 +++
kernel/bpf/syscall.c | 28 ++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b69e7a5869ff..ca3e6ff7091d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -53,6 +53,9 @@ struct bpf_map {
struct work_struct work;
atomic_t usercnt;
struct bpf_map *inner_map_meta;
+#ifdef CONFIG_SECURITY
+ void *security;
+#endif
};
/* function argument constraints */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 045646da97cc..b15580bcf3b1 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -279,6 +279,10 @@ static int map_create(union bpf_attr *attr)
if (err)
return -EINVAL;
+ err = security_map_create();

Seems a bit limited to me, don't you want to be able to
also differentiate between different map types? Same goes
for security_prog_load() wrt prog types, no?

+ if (err)
+ return -EACCES;
+
/* find map type and init map: hashtable vs rbtree vs bloom vs ... */
map = find_and_alloc_map(attr);
if (IS_ERR(map))
@@ -291,6 +295,10 @@ static int map_create(union bpf_attr *attr)
if (err)
goto free_map_nouncharge;
+ err = security_post_create(map);
+ if (err < 0)
+ goto free_map;
+

So the hook you implement in patch 3/3 does:

+static int selinux_bpf_post_create(struct bpf_map *map)
+{
+ struct bpf_security_struct *bpfsec;
+
+ bpfsec = kzalloc(sizeof(*bpfsec), GFP_KERNEL);
+ if (!bpfsec)
+ return -ENOMEM;
+
+ bpfsec->sid = current_sid();
+ map->security = bpfsec;
+
+ return 0;
+}

Where do you kfree() bpfsec when the map gets released
normally or in error path?

err = bpf_map_alloc_id(map);
if (err)
goto free_map;
@@ -410,6 +418,10 @@ static int map_lookup_elem(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_read(map);
+ if (err)
+ return -EACCES;

How about actually dropping ref?

+
key = memdup_user(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
@@ -490,6 +502,10 @@ static int map_update_elem(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_modify(map);
+ if (err)
+ return -EACCES;

Ditto ...

key = memdup_user(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
@@ -573,6 +589,10 @@ static int map_delete_elem(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_modify(map);
+ if (err)
+ return -EACCES;

Ditto ...

key = memdup_user(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
@@ -616,6 +636,10 @@ static int map_get_next_key(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);
+ err = security_map_read(map);
+ if (err)
+ return -EACCES;

And once again here ... :(

if (ukey) {
key = memdup_user(ukey, map->key_size);
if (IS_ERR(key)) {
@@ -935,6 +959,10 @@ static int bpf_prog_load(union bpf_attr *attr)
if (CHECK_ATTR(BPF_PROG_LOAD))
return -EINVAL;
+ err = security_prog_load();
+ if (err)
+ return -EACCES;
+
if (attr->prog_flags & ~BPF_F_STRICT_ALIGNMENT)
return -EINVAL;

Chenbo Feng via Selinux

2017-09-01 00:29:42 UTC

Against which tree is this by the way, net-next? There are
changes here which require a rebase of your set.

This patch series is rebased on security subsystem since patch 1/3 is
a patch for
security system I assume. But I am not sure where this specific patch
should go in.
If I should submit this one to net-next, I will rebase it against
net-next and submit again.

Seems a bit limited to me, don't you want to be able to
also differentiate between different map types? Same goes
for security_prog_load() wrt prog types, no?

I don't want to introduce extra complexity into it if not necessary.
so I only included the
thing needed for the selinux implementation for now. But I agree that the map
and program type information could be useful when people developing more complex
security checks. I will add a union bpf_attr *attr pointer into the
security hook functions
for future needs.

+static int selinux_bpf_post_create(struct bpf_map *map)
+{
+ struct bpf_security_struct *bpfsec;
+
+ bpfsec = kzalloc(sizeof(*bpfsec), GFP_KERNEL);
+ if (!bpfsec)
+ return -ENOMEM;
+
+ bpfsec->sid = current_sid();
+ map->security = bpfsec;
+
+ return 0;
+}
Where do you kfree() bpfsec when the map gets released
normally or in error path?

Will add it in next version. Thanks for point it out.

How about actually dropping ref?

May bad, thanks again.

Ditto ...

And once again here ... :(

Chenbo Feng via Selinux

2017-09-05 21:59:38 UTC

On Thu, Aug 31, 2017 at 7:05 PM, Alexei Starovoitov

...

Thanks for pointing out this. I agree we should only do checks on
creating and passing
the object from one processes to another. And if we can still
distinguish the read/write operation
when obtaining the file fd, that would be great. But that may require
us to add a new mode
field into bpf_map struct and change the attribute struct when doing
the bpf syscall. How do you
think about this approach? Or we can do simple checks for
bpf_obj_create and bpf_obj_use when
creating the object and passing the object respectively but this
solution cannot distinguish map modify and
read.

Alexei Starovoitov

2017-09-06 00:39:14 UTC