bpf,lsm: add BPF token LSM hooks

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>
Link: https://lore.kernel.org/r/20231130185229.2688956-12-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -1604,6 +1604,9 @@ struct bpf_token {
 	u64 allowed_maps;
 	u64 allowed_progs;
 	u64 allowed_attachs;
+#ifdef CONFIG_SECURITY
+	void *security;
+#endif
 };
 
 struct bpf_struct_ops_value;

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)

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 */
 

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)

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)

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 */
 
 /**