crond: implement support for setting PATH in crontab files

It's very inconvenient for a cron user not to be able to set a
"personal" PATH for their cron jobs, as is possible with other crons

function                                             old     new   delta
load_crontab                                         868     942     +74
.rodata                                           104878  104884      +6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 80/0)               Total: 80 bytes

Signed-off-by: Paul Fox <pgf@foxharp.boston.ma.us>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

miscutils/crond.c

@@ -125,6 +125,7 @@ typedef struct CronLine {
 	char *cl_mailto;                /* whom to mail results, may be NULL */
 #endif
 	char *cl_shell;
+	char *cl_path;
 	/* ordered by size, not in natural order. makes code smaller: */
 	char cl_Dow[7];                 /* 0-6, beginning sunday */
 	char cl_Mons[12];               /* 0-11 */
@@ -421,6 +422,7 @@ static void load_crontab(const char *fileName)
 	char *mailTo = NULL;
 #endif
 	char *shell = NULL;
+	char *path = NULL;
 
 	delete_cronfile(fileName);
 
@@ -470,7 +472,12 @@ static void load_crontab(const char *fileName)
 				shell = xstrdup(&tokens[0][6]);
 				continue;
 			}
-//TODO: handle HOME= too? "man crontab" says:
+			if (is_prefixed_with(tokens[0], "PATH=")) {
+				free(path);
+				path = xstrdup(&tokens[0][5]);
+				continue;
+			}
+//TODO: handle HOME= too? Better yet, handle arbitrary ENVVARs? "man crontab" says:
 //name = value
 //
 //where the spaces around the equal-sign (=) are optional, and any subsequent
@@ -480,8 +487,8 @@ static void load_crontab(const char *fileName)
 //
 //Several environment variables are set up automatically by the cron(8) daemon.
 //SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd
-//line of the crontab's owner. HOME and SHELL may be overridden by settings
+//line of the crontab's owner.  HOME, SHELL, and PATH may be overridden by
-//in the crontab; LOGNAME may not.
+//settings in the crontab; LOGNAME may not.
 
 #if ENABLE_FEATURE_CROND_SPECIAL_TIMES
 			if (tokens[0][0] == '@') {
@@ -567,6 +574,7 @@ static void load_crontab(const char *fileName)
 			line->cl_mailto = xstrdup(mailTo);
 #endif
 			line->cl_shell = xstrdup(shell);
+			line->cl_path = xstrdup(path);
 			/* copy command */
 			line->cl_cmd = xstrdup(tokens[5]);
 			pline = &line->cl_next;
@@ -653,21 +661,22 @@ static void safe_setenv(char **pvar_val, const char *var, const char *val)
 }
 #endif
 
-static void set_env_vars(struct passwd *pas, const char *shell)
+static void set_env_vars(struct passwd *pas, const char *shell, const char *path)
 {
 	/* POSIX requires crond to set up at least HOME, LOGNAME, PATH, SHELL.
-	 * We assume crond inherited suitable PATH.
 	 */
 #if SETENV_LEAKS
 	safe_setenv(&G.env_var_logname, "LOGNAME", pas->pw_name);
 	safe_setenv(&G.env_var_user, "USER", pas->pw_name);
 	safe_setenv(&G.env_var_home, "HOME", pas->pw_dir);
 	safe_setenv(&G.env_var_shell, "SHELL", shell);
+	if (path) safe_setenv(&G.env_var_shell, "PATH", path);
 #else
 	xsetenv("LOGNAME", pas->pw_name);
 	xsetenv("USER", pas->pw_name);
 	xsetenv("HOME", pas->pw_dir);
 	xsetenv("SHELL", shell);
+	if (path) xsetenv("PATH", path);
 #endif
 }
 
@@ -701,7 +710,7 @@ fork_job(const char *user, int mailFd, CronLine *line, bool run_sendmail)
 	shell = line->cl_shell ? line->cl_shell : G.default_shell;
 	prog = run_sendmail ? SENDMAIL : shell;
 
-	set_env_vars(pas, shell);
+	set_env_vars(pas, shell, NULL); /* don't use crontab's PATH for sendmail */
 
 	sv_logmode = logmode;
 	pid = vfork();
@@ -845,7 +854,7 @@ static pid_t start_one_job(const char *user, CronLine *line)
 
 	/* Prepare things before vfork */
 	shell = line->cl_shell ? line->cl_shell : G.default_shell;
-	set_env_vars(pas, shell);
+	set_env_vars(pas, shell, line->cl_path);
 
 	/* Fork as the user in question and run program */
 	pid = vfork();