[PATCH bpf-next 11/29] bpf,lsm: add BPF token LSM hooks

Andrii Nakryiko
2024-01-03T22:21:45Z

Wire up bpf_token_create and bpf_token_free LSM hooks, which allow to
allocate LSM security blob (we add `void *security` field to struct
bpf_token for that), but also control who can instantiate BPF token.
This follows existing pattern for BPF map and BPF prog.

Also add security_bpf_token_allow_cmd() and security_bpf_token_capable()
LSM hooks that allow LSM implementation to control and negate (if
necessary) BPF token's delegation of a specific bpf_cmd and capability,
respectively.

Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
include/linux/bpf.h | 3 ++
include/linux/lsm_hook_defs.h | 5 +++
include/linux/security.h | 25 +++++++++++++++
kernel/bpf/bpf_lsm.c | 4 +++
kernel/bpf/token.c | 18 +++++++----
security/security.c | 60 +++++++++++++++++++++++++++++++++++
6 files changed, 109 insertions(+), 6 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index d1023cd67f65..778d07bb7240 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1633,6 +1633,9 @@ struct bpf_token {
u64 allowed_maps;
u64 allowed_progs;
u64 allowed_attachs;
+#ifdef CONFIG_SECURITY
+ void *security;
+#endif
};

struct bpf_struct_ops_value;
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index adb25cc63ce3..3fdd00b452ac 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -404,6 +404,11 @@ LSM_HOOK(void, LSM_RET_VOID, bpf_map_free, struct bpf_map *map)
LSM_HOOK(int, 0, bpf_prog_load, struct bpf_prog *prog, union bpf_attr *attr,
struct bpf_token *token)
LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free, struct bpf_prog *prog)
+LSM_HOOK(int, 0, bpf_token_create, struct bpf_token *token, union bpf_attr *attr,
+ struct path *path)
+LSM_HOOK(void, LSM_RET_VOID, bpf_token_free, struct bpf_token *token)
+LSM_HOOK(int, 0, bpf_token_cmd, const struct bpf_token *token, enum bpf_cmd cmd)
+LSM_HOOK(int, 0, bpf_token_capable, const struct bpf_token *token, int cap)
#endif /* CONFIG_BPF_SYSCALL */

LSM_HOOK(int, 0, locked_down, enum lockdown_reason what)
diff --git a/include/linux/security.h b/include/linux/security.h
index 08fd777cbe94..00809d2d5c38 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -32,6 +32,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/sockptr.h>
+#include <linux/bpf.h>

struct linux_binprm;
struct cred;
@@ -2031,6 +2032,11 @@ extern void security_bpf_map_free(struct bpf_map *map);
extern int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
struct bpf_token *token);
extern void security_bpf_prog_free(struct bpf_prog *prog);
+extern int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
+ struct path *path);
+extern void security_bpf_token_free(struct bpf_token *token);
+extern int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd);
+extern int security_bpf_token_capable(const struct bpf_token *token, int cap);
#else
static inline int security_bpf(int cmd, union bpf_attr *attr,
unsigned int size)
@@ -2065,6 +2071,25 @@ static inline int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *

static inline void security_bpf_prog_free(struct bpf_prog *prog)
{ }
+
+static inline int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
+ struct path *path)
+{
+ return 0;
+}
+
+static inline void security_bpf_token_free(struct bpf_token *token)
+{ }
+
+static inline int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
+{
+ return 0;
+}
+
+static inline int security_bpf_token_capable(const struct bpf_token *token, int cap)
+{
+ return 0;
+}
#endif /* CONFIG_SECURITY */
#endif /* CONFIG_BPF_SYSCALL */

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 76976908b302..63b4dc495125 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -265,6 +265,10 @@ BTF_ID(func, bpf_lsm_bpf_map_free)
BTF_ID(func, bpf_lsm_bpf_prog)
BTF_ID(func, bpf_lsm_bpf_prog_load)
BTF_ID(func, bpf_lsm_bpf_prog_free)
+BTF_ID(func, bpf_lsm_bpf_token_create)
+BTF_ID(func, bpf_lsm_bpf_token_free)
+BTF_ID(func, bpf_lsm_bpf_token_cmd)
+BTF_ID(func, bpf_lsm_bpf_token_capable)
BTF_ID(func, bpf_lsm_bprm_check_security)
BTF_ID(func, bpf_lsm_bprm_committed_creds)
BTF_ID(func, bpf_lsm_bprm_committing_creds)
diff --git a/kernel/bpf/token.c b/kernel/bpf/token.c
index 5a51e6b8f6bf..17212efcde60 100644
--- a/kernel/bpf/token.c
+++ b/kernel/bpf/token.c
@@ -7,6 +7,7 @@
#include <linux/idr.h>
#include <linux/namei.h>
#include <linux/user_namespace.h>
+#include <linux/security.h>

bool bpf_token_capable(const struct bpf_token *token, int cap)
{
@@ -14,10 +15,9 @@ bool bpf_token_capable(const struct bpf_token *token, int cap)
* token's userns is *exactly* the same as current user's userns
*/
if (token && current_user_ns() == token->userns) {
- if (ns_capable(token->userns, cap))
- return true;
- if (cap != CAP_SYS_ADMIN && ns_capable(token->userns, CAP_SYS_ADMIN))
- return true;
+ if (ns_capable(token->userns, cap) ||
+ (cap != CAP_SYS_ADMIN && ns_capable(token->userns, CAP_SYS_ADMIN)))
+ return security_bpf_token_capable(token, cap) == 0;
}
/* otherwise fallback to capable() checks */
return capable(cap) || (cap != CAP_SYS_ADMIN && capable(CAP_SYS_ADMIN));
@@ -30,6 +30,7 @@ void bpf_token_inc(struct bpf_token *token)

static void bpf_token_free(struct bpf_token *token)
{
+ security_bpf_token_free(token);
put_user_ns(token->userns);
kvfree(token);
}
@@ -186,6 +187,10 @@ int bpf_token_create(union bpf_attr *attr)
token->allowed_progs = mnt_opts->delegate_progs;
token->allowed_attachs = mnt_opts->delegate_attachs;

+ err = security_bpf_token_create(token, attr, &path);
+ if (err)
+ goto out_token;
+
fd = get_unused_fd_flags(O_CLOEXEC);
if (fd < 0) {
err = fd;
@@ -233,8 +238,9 @@ bool bpf_token_allow_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
*/
if (!token || current_user_ns() != token->userns)
return false;
-
- return token->allowed_cmds & (1ULL << cmd);
+ if (!(token->allowed_cmds & (1ULL << cmd)))
+ return false;
+ return security_bpf_token_cmd(token, cmd) == 0;
}

bool bpf_token_allow_map_type(const struct bpf_token *token, enum bpf_map_type type)
diff --git a/security/security.c b/security/security.c
index ad24cf36da94..088a79c35c26 100644
--- a/security/security.c
+++ b/security/security.c
@@ -5201,6 +5201,55 @@ int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
return call_int_hook(bpf_prog_load, 0, prog, attr, token);
}

+/**
+ * security_bpf_token_create() - Check if creating of BPF token is allowed
+ * @token: BPF token object
+ * @attr: BPF syscall attributes used to create BPF token
+ * @path: path pointing to BPF FS mount point from which BPF token is created
+ *
+ * Do a check when the kernel instantiates a new BPF token object from BPF FS
+ * instance. This is also the point where LSM blob can be allocated for LSMs.
+ *
+ * Return: Returns 0 on success, error on failure.
+ */
+int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
+ struct path *path)
+{
+ return call_int_hook(bpf_token_create, 0, token, attr, path);
+}
+
+/**
+ * security_bpf_token_cmd() - Check if BPF token is allowed to delegate
+ * requested BPF syscall command
+ * @token: BPF token object
+ * @cmd: BPF syscall command requested to be delegated by BPF token
+ *
+ * Do a check when the kernel decides whether provided BPF token should allow
+ * delegation of requested BPF syscall command.
+ *
+ * Return: Returns 0 on success, error on failure.
+ */
+int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
+{
+ return call_int_hook(bpf_token_cmd, 0, token, cmd);
+}
+
+/**
+ * security_bpf_token_capable() - Check if BPF token is allowed to delegate
+ * requested BPF-related capability
+ * @token: BPF token object
+ * @cap: capabilities requested to be delegated by BPF token
+ *
+ * Do a check when the kernel decides whether provided BPF token should allow
+ * delegation of requested BPF-related capabilities.
+ *
+ * Return: Returns 0 on success, error on failure.
+ */
+int security_bpf_token_capable(const struct bpf_token *token, int cap)
+{
+ return call_int_hook(bpf_token_capable, 0, token, cap);
+}
+
/**
* security_bpf_map_free() - Free a bpf map's LSM blob
* @map: bpf map
@@ -5222,6 +5271,17 @@ void security_bpf_prog_free(struct bpf_prog *prog)
{
call_void_hook(bpf_prog_free, prog);
}
+
+/**
+ * security_bpf_token_free() - Free a BPF token's LSM blob
+ * @token: BPF token struct
+ *
+ * Clean up the security information stored inside BPF token.
+ */
+void security_bpf_token_free(struct bpf_token *token)
+{
+ call_void_hook(bpf_token_free, token);
+}
#endif /* CONFIG_BPF_SYSCALL */

/**
--
2.34.1