Add intercept_type sudoers option to set intercept/log_subcmds mechanism.

docs/sudoers.man.in

@@ -25,7 +25,7 @@
 .nr BA @BAMAN@
 .nr LC @LCMAN@
 .nr PS @PSMAN@
-.TH "SUDOERS" "@mansectform@" "May 4, 2022" "Sudo @PACKAGE_VERSION@" "File Formats Manual"
+.TH "SUDOERS" "@mansectform@" "May 24, 2022" "Sudo @PACKAGE_VERSION@" "File Formats Manual"
 .nh
 .if n .ad l
 .SH "NAME"
@@ -3307,18 +3307,20 @@ To prevent this from happening,
 will not permit a set-user-ID or set-group-ID program to be run in
 intercept mode unless
 \fIintercept_allow_setid\fR
-is set.
+is enable.
 This flag has no effect unless the
 \fIintercept\fR
 flag is enabled or the
 \fIINTERCEPT\fR
 tag has been set for the command.
 This flag is
-\fIoff\fR
-by default except on Linux systems that support
-seccomp(2)
-filtering, where it defaults to
-\fIon\fR.
+\fIon\fR
+by default when the
+\fIintercept_type\fR
+option is set to
+\fItrace\fR,
+otherwise it default to
+\fIoff\fR.
 .sp
 This setting is only supported by version 1.9.8 or higher.
 .TP 18n
@@ -4215,6 +4217,63 @@ option is disabled.
 The default is
 \fI@editor@\fR.
 .TP 18n
+intercept_type
+The underlying mechanism used by the
+\fIintercept\fR
+and
+\fIlog_subcmds\fR
+options.
+It has the following possible values:
+.PP
+.RS 18n
+.PD 0
+.TP 8n
+dso
+Preload a dynamic shared object (shared library) that intercepts the
+\fBexecl\fR(),
+\fBexecle\fR(),
+\fBexeclp\fR(),
+\fBexecv\fR(),
+\fBexecve\fR(),
+\fBexecvp\fR(),
+and
+\fBexecvpe\fR()
+library functions.
+A value of
+\fIdso\fR
+is incompatible with
+\fBsudo\fR's
+SELinux RBAC support.
+.PD
+.TP 8n
+trace
+Use
+ptrace(2)
+to intercept the
+execve(2)
+system call.
+This is only supported on Linux systems where
+seccomp(2)
+filtering is enabled.
+If the
+\fI/proc/sys/kernel/seccomp/actions_avail\fR
+file is missing or does not contain a
+\(lqtrap\(rq
+element, setting
+\fIintercept_type\fR
+to
+\fItrace\fR
+will have no effect and
+\fIdso\fR
+will be used instead.
+.PP
+The default is to use
+\fItrace\fR
+if it is supported by the system and
+\fIdso\fR
+if it is not.
+.RE
+.TP 18n
 iolog_dir
 The top-level directory to use when constructing the path name for
 the input/output log directory.
@@ -6777,7 +6836,7 @@ by default and interferes with file descriptor inheritance.
 .sp
 Linux systems that support
 seccomp(2)
-filtering will use a different method involving
+filtering can use a different method involving
 ptrace(2)
 instead of pre-loading a shared library.
 This method supports both static and dynamic executables as well as

docs/sudoers.mdoc.in

@@ -24,7 +24,7 @@
 .nr BA @BAMAN@
 .nr LC @LCMAN@
 .nr PS @PSMAN@
-.Dd May 4, 2022
+.Dd May 24, 2022
 .Dt SUDOERS @mansectform@
 .Os Sudo @PACKAGE_VERSION@
 .Sh NAME
@@ -3123,18 +3123,20 @@ To prevent this from happening,
 will not permit a set-user-ID or set-group-ID program to be run in
 intercept mode unless
 .Em intercept_allow_setid
-is set.
+is enable.
 This flag has no effect unless the
 .Em intercept
 flag is enabled or the
 .Em INTERCEPT
 tag has been set for the command.
 This flag is
-.Em off
-by default except on Linux systems that support
-.Xr seccomp 2
-filtering, where it defaults to
-.Em on .
+.Em on
+by default when the
+.Em intercept_type
+option is set to
+.Em trace ,
+otherwise it default to
+.Em off .
 .Pp
 This setting is only supported by version 1.9.8 or higher.
 .It intercept_authenticate
@@ -3982,6 +3984,57 @@ list or the
 option is disabled.
 The default is
 .Pa @editor@ .
+.It intercept_type
+The underlying mechanism used by the
+.Em intercept
+and
+.Em log_subcmds
+options.
+It has the following possible values:
+.Bl -tag -width 6n
+.It dso
+Preload a dynamic shared object (shared library) that intercepts the
+.Fn execl ,
+.Fn execle ,
+.Fn execlp ,
+.Fn execv ,
+.Fn execve ,
+.Fn execvp ,
+and
+.Fn execvpe
+library functions.
+A value of
+.Em dso
+is incompatible with
+.Nm sudo Ns 's
+SELinux RBAC support.
+.It trace
+Use
+.Xr ptrace 2
+to intercept the
+.Xr execve 2
+system call.
+This is only supported on Linux systems where
+.Xr seccomp 2
+filtering is enabled.
+If the
+.Pa /proc/sys/kernel/seccomp/actions_avail
+file is missing or does not contain a
+.Dq trap
+element, setting
+.Em intercept_type
+to
+.Em trace
+will have no effect and
+.Em dso
+will be used instead.
+.El
+.Pp
+The default is to use
+.Em trace
+if it is supported by the system and
+.Em dso
+if it is not.
 .It iolog_dir
 The top-level directory to use when constructing the path name for
 the input/output log directory.
@@ -6266,7 +6319,7 @@ by default and interferes with file descriptor inheritance.
 .Pp
 Linux systems that support
 .Xr seccomp 2
-filtering will use a different method involving
+filtering can use a different method involving
 .Xr ptrace 2
 instead of pre-loading a shared library.
 This method supports both static and dynamic executables as well as

plugins/sudoers/def_data.c

@@ -44,6 +44,12 @@ static struct def_values def_data_log_format[] = {
     { NULL, 0 },
 };
 
+static struct def_values def_data_intercept_type[] = {
+    { "dso", dso },
+    { "trace", trace },
+    { NULL, 0 },
+};
+
 struct sudo_defs_types sudo_defs_table[] = {
     {
 	"syslog", T_LOGFAC|T_BOOL,
@@ -657,6 +663,10 @@ struct sudo_defs_types sudo_defs_table[] = {
 	"passprompt_regex", T_LIST|T_SPACE|T_BOOL,
 	N_("List of regular expressions to use when matching a password prompt"),
 	NULL,
+    }, {
+	"intercept_type", T_TUPLE,
+	N_("The mechanism used by the intercept and log_subcmds options: %s"),
+	def_data_intercept_type,
     }, {
 	NULL, 0, NULL
     }

plugins/sudoers/def_data.h

@@ -306,6 +306,8 @@
 #define def_log_passwords       (sudo_defs_table[I_LOG_PASSWORDS].sd_un.flag)
 #define I_PASSPROMPT_REGEX      152
 #define def_passprompt_regex    (sudo_defs_table[I_PASSPROMPT_REGEX].sd_un.list)
+#define I_INTERCEPT_TYPE        153
+#define def_intercept_type      (sudo_defs_table[I_INTERCEPT_TYPE].sd_un.tuple)
 
 enum def_tuple {
     never,
@@ -319,5 +321,7 @@ enum def_tuple {
     tty,
     kernel,
     sudo,
-    json
+    json,
+    dso,
+    trace
 };

plugins/sudoers/def_data.in

@@ -475,3 +475,7 @@ log_passwords
 passprompt_regex
 	T_LIST|T_SPACE|T_BOOL
 	"List of regular expressions to use when matching a password prompt"
+intercept_type
+	T_TUPLE
+	"The mechanism used by the intercept and log_subcmds options: %s"
+	dso trace

plugins/sudoers/defaults.c

@@ -548,8 +548,7 @@ init_defaults(void)
 #endif
     if ((def_rlimit_core = strdup("0,0")) == NULL)
 	goto oom;
-    if (ISSET(sudo_user.flags, CAN_INTERCEPT_SETID))
-	def_intercept_allow_setid = true;
+    def_intercept_type = dso;
     def_netgroup_tuple = false;
     def_sudoedit_checkdir = true;
     def_iolog_mode = S_IRUSR|S_IWUSR;

plugins/sudoers/policy.c

@@ -297,10 +297,24 @@ sudoers_policy_deserialize_info(void *v, struct defaults_list *defaults)
 		goto oom;
 	    continue;
 	}
+	if (MATCHES(*cur, "intercept_ptrace=")) {
+	    int val = sudo_strtobool(*cur + sizeof("intercept_ptrace=") - 1);
+	    if (val == -1) {
+		INVALID("intercept_ptrace=");	/* Not a fatal error. */
+	    } else if (!append_default("intercept_type",
+		    val ? "trace" : "dso", true, NULL, defaults)) {
+		goto oom;
+	    }
+	    continue;
+	}
 	if (MATCHES(*cur, "intercept_setid=")) {
-	    if (parse_bool(*cur, sizeof("intercept_setid") - 1,
-		&sudo_user.flags, CAN_INTERCEPT_SETID) == -1)
-		goto bad;
+	    int val = sudo_strtobool(*cur + sizeof("intercept_setid=") - 1);
+	    if (val == -1) {
+		INVALID("intercept_setid=");	/* Not a fatal error. */
+	    } else if (!append_default("intercept_allow_setid", NULL, val,
+		    NULL, defaults)) {
+		goto oom;
+	    }
 	    continue;
 	}
 #ifdef HAVE_SELINUX
@@ -605,7 +619,7 @@ sudoers_policy_store_result(bool accepted, char *argv[], char *envp[],
     }
 
     /* Increase the length of command_info as needed, it is *not* checked. */
-    command_info = calloc(70, sizeof(char *));
+    command_info = calloc(71, sizeof(char *));
     if (command_info == NULL)
 	goto oom;
 
@@ -777,6 +791,10 @@ sudoers_policy_store_result(bool accepted, char *argv[], char *envp[],
 	if ((command_info[info_len++] = strdup("intercept=true")) == NULL)
 	    goto oom;
     }
+    if (def_intercept_type == trace) {
+	if ((command_info[info_len++] = strdup("use_ptrace=true")) == NULL)
+	    goto oom;
+    }
     if (def_noexec) {
 	if ((command_info[info_len++] = strdup("noexec=true")) == NULL)
 	    goto oom;

plugins/sudoers/sudoers.h

@@ -145,7 +145,6 @@ struct sudo_user {
  */
 #define RUNAS_USER_SPECIFIED	0x01
 #define RUNAS_GROUP_SPECIFIED	0x02
-#define CAN_INTERCEPT_SETID	0x04
 
 /*
  * Return values for sudoers_lookup(), also used as arguments for log_auth()

src/exec_ptrace.c

@@ -51,6 +51,8 @@
 # include "exec_intercept.h"
 # include "exec_ptrace.h"
 
+static int seccomp_trap_supported = -1;
+
 /* Register getters and setters. */
 # ifdef SECCOMP_AUDIT_ARCH_COMPAT
 static inline unsigned long
@@ -736,7 +738,7 @@ done:
  * Check whether seccomp(2) filtering supports ptrace(2) traps.
  * Only supported by Linux 4.14 and higher.
  */
-bool
+static bool
 have_seccomp_action(const char *action)
 {
     char line[LINE_MAX];
@@ -1274,6 +1276,24 @@ exec_ptrace_stopped(pid_t pid, int status, void *intercept)
 
     debug_return_bool(group_stop);
 }
+
+bool
+exec_ptrace_intercept_supported(void)
+{
+    if (seccomp_trap_supported == -1)
+	seccomp_trap_supporetd = have_seccomp_action("trap");
+
+    return seccomp_trap_supported == true;
+}
+
+bool
+exec_ptrace_subcmds_supported(void)
+{
+    if (seccomp_trap_supported == -1)
+	seccomp_trap_supported = have_seccomp_action("trap");
+
+    return seccomp_trap_supported == true;
+}
 #else
 /* STUB */
 bool
@@ -1295,4 +1315,41 @@ exec_ptrace_seize(pid_t child)
 {
     return true;
 }
+
+/* STUB */
+bool
+exec_ptrace_intercept_supported(void)
+{
+    return false;
+}
+
+/* STUB */
+bool
+exec_ptrace_subcmds_supported(void)
+{
+    return false;
+}
 #endif /* HAVE_PTRACE_INTERCEPT */
+
+/*
+ * Adjust flags based on the availability of ptrace support.
+ */
+void
+exec_ptrace_fix_flags(struct command_details *details)
+{
+    debug_decl(exec_ptrace_fix_flags, SUDO_DEBUG_EXEC);
+
+    if (ISSET(details->flags, CD_USE_PTRACE)) {
+	/* If both CD_INTERCEPT and CD_LOG_SUBCMDS set, CD_INTERCEPT wins. */
+	if (ISSET(details->flags, CD_INTERCEPT)) {
+	    if (!exec_ptrace_intercept_supported())
+		CLR(details->flags, CD_USE_PTRACE);
+	} else if (ISSET(details->flags, CD_LOG_SUBCMDS)) {
+	    if (!exec_ptrace_subcmds_supported())
+		CLR(details->flags, CD_USE_PTRACE);
+	} else {
+	    CLR(details->flags, CD_USE_PTRACE);
+	}
+    }
+    debug_return;
+}

src/parse_args.c

@@ -82,6 +82,7 @@ static struct sudo_settings sudo_settings[] = {
     { "cmnd_cwd" },
     { "askpass" },
     { "intercept_setid" },
+    { "intercept_ptrace" },
     { NULL }
 };
 
@@ -585,8 +586,10 @@ parse_args(int argc, char **argv, int *old_optind, int *nargc, char ***nargv,
 #ifdef ENABLE_SUDO_PLUGIN_API
     sudo_settings[ARG_PLUGIN_DIR].value = sudo_conf_plugin_dir_path();
 #endif
-    if (have_seccomp_action("trap"))
+    if (exec_ptrace_intercept_supported())
 	sudo_settings[ARG_INTERCEPT_SETID].value = "true";
+    if (exec_ptrace_subcmds_supported())
+	sudo_settings[ARG_INTERCEPT_PTRACE].value = "true";
 
     if (mode == MODE_HELP)
 	help();

src/sudo.c

@@ -650,10 +650,10 @@ bad:
 static void
 command_info_to_details(char * const info[], struct command_details *details)
 {
-    int i;
-    id_t id;
-    char *cp;
     const char *errstr;
+    char *cp;
+    id_t id;
+    int i;
     debug_decl(command_info_to_details, SUDO_DEBUG_PCOMM);
 
     memset(details, 0, sizeof(*details));
@@ -857,17 +857,15 @@ command_info_to_details(char * const info[], struct command_details *details)
 		    break;
 		}
 		SET_FLAG("umask_override=", CD_OVERRIDE_UMASK)
+		SET_FLAG("use_ptrace=", CD_USE_PTRACE)
 		SET_FLAG("use_pty=", CD_USE_PTY)
 		SET_STRING("utmp_user=", utmp_user)
 		break;
 	}
     }
 
-    if (ISSET(details->flags, CD_INTERCEPT|CD_LOG_SUBCMDS)) {
-	/* Use ptrace(2) for intercept/log_subcmds if possible. */
-	if (sudo_settings[ARG_INTERCEPT_SETID].value != NULL)
-	    SET(details->flags, CD_USE_PTRACE);
-    }
+    /* Only use ptrace(2) for intercept/log_subcmds if supported. */
+    exec_ptrace_fix_flags(details);
 
     if (!ISSET(details->flags, CD_SET_EUID))
 	details->cred.euid = details->cred.uid;

src/sudo.h

@@ -103,6 +103,7 @@
 #define ARG_CWD			24
 #define ARG_ASKPASS		25
 #define ARG_INTERCEPT_SETID	26
+#define ARG_INTERCEPT_PTRACE	27
 
 /*
  * Flags for tgetpass()
@@ -338,6 +339,8 @@ int serialize_rlimits(char **info, size_t info_max);
 bool parse_policy_rlimit(const char *str);
 
 /* exec_ptrace.c */
-bool have_seccomp_action(const char *action);
+void exec_ptrace_fix_flags(struct command_details *details);
+bool exec_ptrace_intercept_supported(void);
+bool exec_ptrace_subcmds_supported(void);
 
 #endif /* SUDO_SUDO_H */

src/sudo_exec.h

@@ -92,7 +92,6 @@ union sudo_token_un {
 
 /*
  * Use ptrace-based intercept (using seccomp) on Linux if possible.
- * TODO: test other architectures
  */
 #if defined(_PATH_SUDO_INTERCEPT) && defined(__linux__)
 # if defined(HAVE_DECL_SECCOMP_SET_MODE_FILTER) && HAVE_DECL_SECCOMP_SET_MODE_FILTER
@@ -100,7 +99,7 @@ union sudo_token_un {
 #   ifndef HAVE_PTRACE_INTERCEPT
 #    define HAVE_PTRACE_INTERCEPT 1
 #   endif /* HAVE_PTRACE_INTERCEPT */
-#  endif /* __amd64__ || __i386__ || __aarch64__ || __riscv */
+#  endif /* __amd64__ || __i386__ || __aarch64__ || __riscv || __s390__ */
 # endif /* HAVE_DECL_SECCOMP_SET_MODE_FILTER */
 #endif /* _PATH_SUDO_INTERCEPT && __linux__ */