noexec: set comm field for noexecs

function                                             old     new   delta
set_task_comm                                          -      18     +18
tryexec                                              152     159      +7
pseudo_exec_argv                                     321     328      +7
main                                                 106      97      -9
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/2 up/down: 34/-13)             Total: 23 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

include/libbb.h

@@ -1116,6 +1116,11 @@ int run_nofork_applet(int applet_no, char **argv) FAST_FUNC;
 extern int find_applet_by_name(const char *name) FAST_FUNC;
 extern void run_applet_no_and_exit(int a, const char *name, char **argv) NORETURN FAST_FUNC;
 #endif
+#if defined(__linux__)
+void set_task_comm(const char *comm) FAST_FUNC;
+#else
+# define set_task_comm(name) ((void)0)
+#endif
 
 /* Helpers for daemonization.
  *

libbb/appletlib.c

@@ -911,6 +911,14 @@ int busybox_main(int argc UNUSED_PARAM, char **argv)
 }
 # endif
 
+#if defined(__linux__) && (NUM_APPLETS > 1)
+void FAST_FUNC set_task_comm(const char *comm)
+{
+	/* okay if too long (truncates) */
+	prctl(PR_SET_NAME, (long)comm, 0, 0, 0);
+}
+#endif
+
 # if NUM_APPLETS > 0
 void FAST_FUNC run_applet_no_and_exit(int applet_no, const char *name, char **argv)
 {
@@ -1064,15 +1072,14 @@ int main(int argc UNUSED_PARAM, char **argv)
 		applet_name++;
 	applet_name = bb_basename(applet_name);
 
-# if defined(__linux__)
 	/* If we are a result of execv("/proc/self/exe"), fix ugly comm of "exe" */
 	if (ENABLE_FEATURE_SH_STANDALONE
 	 || ENABLE_FEATURE_PREFER_APPLETS
 	 || !BB_MMU
 	) {
-		prctl(PR_SET_NAME, (long)applet_name, 0, 0, 0);
+		if (NUM_APPLETS > 1)
+			set_task_comm(applet_name);
 	}
-# endif
 
 	parse_config_file(); /* ...maybe, if FEATURE_SUID_CONFIG */
 	run_applet_and_exit(applet_name, argv);

libbb/vfork_daemon_rexec.c

@@ -175,8 +175,6 @@ int FAST_FUNC spawn_and_wait(char **argv)
 				return wait4pid(rc);
 
 			/* child */
-//TODO: prctl(PR_SET_NAME, (long)argv[0], 0, 0, 0);? [think pidof, pgrep, pkill]
-//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
 			/* reset some state and run without execing */
 
 			/* msg_eol = "\n"; - no caller needs this reinited yet */
@@ -185,6 +183,11 @@ int FAST_FUNC spawn_and_wait(char **argv)
 			 * init, or a NOFORK applet. But none of those call us
 			 * as of yet (and that should probably always stay true).
 			 */
+//TODO: think pidof, pgrep, pkill!
+//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
+//but one from procps-ng-3.3.10 needs more!
+//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
+			set_task_comm(argv[0]);
 			/* xfunc_error_retval and applet_name are init by: */
 			run_applet_no_and_exit(a, argv[0], argv);
 		}

shell/ash.c

@@ -7803,8 +7803,11 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) const char *cmd, char **argv, c
 			while (*envp)
 				putenv(*envp++);
 			popredir(/*drop:*/ 1);
-//TODO: prctl(PR_SET_NAME, (long)argv[0], 0, 0, 0);? [think pidof, pgrep, pkill]
+//TODO: think pidof, pgrep, pkill!
+//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
+//but one from procps-ng-3.3.10 needs more!
 //Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
+			set_task_comm(argv[0]);
 			run_applet_no_and_exit(applet_no, cmd, argv);
 		}
 		/* re-exec ourselves with the new arguments */

shell/hush.c

@@ -7387,8 +7387,11 @@ static NOINLINE void pseudo_exec_argv(nommu_save_t *nommu_save,
 				/* Without this, "rm -i FILE" can't be ^C'ed: */
 				switch_off_special_sigs(G.special_sig_mask);
 				debug_printf_exec("running applet '%s'\n", argv[0]);
-//TODO: prctl(PR_SET_NAME, (long)argv[0], 0, 0, 0);? [think pidof, pgrep, pkill]
+//TODO: think pidof, pgrep, pkill!
+//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
+//but one from procps-ng-3.3.10 needs more!
 //Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
+				set_task_comm(argv[0]);
 				run_applet_no_and_exit(a, argv[0], argv);
 			}
 # endif