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Message-Id: <20160914072415.26021-22-mic@digikod.net>
Date: Wed, 14 Sep 2016 09:24:14 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Mickaël Salaün <mic@...ikod.net>,
Alexei Starovoitov <ast@...nel.org>,
Andy Lutomirski <luto@...capital.net>, Arnd Bergmann <arnd@...db.de>,
Casey Schaufler <casey@...aufler-ca.com>,
Daniel Borkmann <daniel@...earbox.net>,
Daniel Mack <daniel@...que.org>, David Drysdale <drysdale@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
Elena Reshetova <elena.reshetova@...el.com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
James Morris <james.l.morris@...cle.com>,
Kees Cook <keescook@...omium.org>, Paul Moore <pmoore@...hat.com>,
Sargun Dhillon <sargun@...gun.me>,
"Serge E . Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>,
Will Drewry <wad@...omium.org>, kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org, linux-security-module@...r.kernel.org,
netdev@...r.kernel.org, cgroups@...r.kernel.org
Subject: [RFC v3 21/22] bpf,landlock: Add optional skb pointer in the Landlock context
This is a proof of concept to expose optional values that could depend
of the process access rights.
There is two dedicated flags: LANDLOCK_FLAG_ACCESS_SKB_READ and
LANDLOCK_FLAG_ACCESS_SKB_WRITE. Each of them can be activated to access
eBPF functions manipulating a skb in a read or write way.
Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: David S. Miller <davem@...emloft.net>
Cc: Kees Cook <keescook@...omium.org>
Cc: Sargun Dhillon <sargun@...gun.me>
---
include/linux/bpf.h | 2 ++
include/uapi/linux/bpf.h | 7 ++++++-
kernel/bpf/verifier.c | 6 ++++++
security/landlock/lsm.c | 26 ++++++++++++++++++++++++++
4 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f7325c17f720..218973777612 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -88,6 +88,7 @@ enum bpf_arg_type {
ARG_PTR_TO_STRUCT_FILE, /* pointer to struct file */
ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS, /* pointer to Landlock FS handle */
+ ARG_PTR_TO_STRUCT_SKB, /* pointer to struct skb */
};
/* type of values returned from helper functions */
@@ -150,6 +151,7 @@ enum bpf_reg_type {
/* Landlock */
PTR_TO_STRUCT_FILE,
CONST_PTR_TO_LANDLOCK_HANDLE_FS,
+ PTR_TO_STRUCT_SKB,
};
struct bpf_prog;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8cfc2de2ab76..7d9e56952ed9 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -586,7 +586,9 @@ enum landlock_hook_id {
/* context of function access flags */
#define LANDLOCK_FLAG_ACCESS_UPDATE (1 << 0)
#define LANDLOCK_FLAG_ACCESS_DEBUG (1 << 1)
-#define _LANDLOCK_FLAG_ACCESS_MASK ((1ULL << 2) - 1)
+#define LANDLOCK_FLAG_ACCESS_SKB_READ (1 << 2)
+#define LANDLOCK_FLAG_ACCESS_SKB_WRITE (1 << 3)
+#define _LANDLOCK_FLAG_ACCESS_MASK ((1ULL << 4) - 1)
/* Handle check flags */
#define LANDLOCK_FLAG_FS_DENTRY (1 << 0)
@@ -619,12 +621,15 @@ struct landlock_handle {
* @args: LSM hook arguments, see include/linux/lsm_hooks.h for there
* description and the LANDLOCK_HOOK* definitions from
* security/landlock/lsm.c for their types.
+ * @opt_skb: optional skb pointer, accessible with the
+ * LANDLOCK_FLAG_ACCESS_SKB_* flags for network-related hooks.
*/
struct landlock_data {
__u32 hook; /* enum landlock_hook_id */
__u16 origin; /* LANDLOCK_FLAG_ORIGIN_* */
__u16 cookie; /* seccomp RET_LANDLOCK */
__u64 args[6];
+ __u64 opt_skb;
};
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8d7b18574f5a..a95154c1a60f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -247,6 +247,7 @@ static const char * const reg_type_str[] = {
[PTR_TO_PACKET_END] = "pkt_end",
[PTR_TO_STRUCT_FILE] = "struct_file",
[CONST_PTR_TO_LANDLOCK_HANDLE_FS] = "landlock_handle_fs",
+ [PTR_TO_STRUCT_SKB] = "struct_skb",
};
static void print_verifier_state(struct verifier_state *state)
@@ -559,6 +560,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case CONST_PTR_TO_MAP:
case PTR_TO_STRUCT_FILE:
case CONST_PTR_TO_LANDLOCK_HANDLE_FS:
+ case PTR_TO_STRUCT_SKB:
return true;
default:
return false;
@@ -984,6 +986,10 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
expected_type = CONST_PTR_TO_LANDLOCK_HANDLE_FS;
if (type != expected_type)
goto err_type;
+ } else if (arg_type == ARG_PTR_TO_STRUCT_SKB) {
+ expected_type = PTR_TO_STRUCT_SKB;
+ if (type != expected_type)
+ goto err_type;
} else if (arg_type == ARG_PTR_TO_STACK ||
arg_type == ARG_PTR_TO_RAW_STACK) {
expected_type = PTR_TO_STACK;
diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c
index 56c45abe979c..8b0e6f0eb6b7 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -281,6 +281,7 @@ static bool __is_valid_access(int off, int size, enum bpf_access_type type,
break;
case offsetof(struct landlock_data, args[0]) ...
offsetof(struct landlock_data, args[5]):
+ case offsetof(struct landlock_data, opt_skb):
expected_size = sizeof(__u64);
break;
default:
@@ -299,6 +300,13 @@ static bool __is_valid_access(int off, int size, enum bpf_access_type type,
if (*reg_type == NOT_INIT)
return false;
break;
+ case offsetof(struct landlock_data, opt_skb):
+ if (!(prog_subtype->landlock_hook.access &
+ (LANDLOCK_FLAG_ACCESS_SKB_READ |
+ LANDLOCK_FLAG_ACCESS_SKB_WRITE)))
+ return false;
+ *reg_type = PTR_TO_STRUCT_SKB;
+ break;
}
return true;
@@ -401,6 +409,24 @@ static inline bool bpf_landlock_is_valid_subtype(
if (prog_subtype->landlock_hook.access & LANDLOCK_FLAG_ACCESS_DEBUG &&
!capable(CAP_SYS_ADMIN))
return false;
+ /*
+ * Capability checks must be enforced for every landlocked process.
+ * To support user namespaces/capabilities, we must then check the
+ * namespaces of a task before putting it in a landlocked cgroup.
+ * This could be implemented in the future.
+ */
+ if (prog_subtype->landlock_hook.access & LANDLOCK_FLAG_ACCESS_SKB_READ &&
+ !capable(CAP_NET_ADMIN))
+ return false;
+ /*
+ * It is interesting to differentiate read and write access to be able
+ * to securely delegate some work to unprivileged (and potentially
+ * compromised/untrusted) processes. This different type of access can
+ * be checked for function calls or context accesses.
+ */
+ if (prog_subtype->landlock_hook.access & LANDLOCK_FLAG_ACCESS_SKB_WRITE &&
+ !capable(CAP_NET_ADMIN))
+ return false;
return true;
}
--
2.9.3
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