service(8): use an environment more consistent with init(8)

init(8) sets the "daemon" login class without specifying a pw
entry (so no substitutions are done on the variables). service(8)'s
use of env -L had the effect of specifying root's pw entry, with two
effects: getpwnam and getpwuid are being called, which may not be
entirely safe depending on what nsswitch is up to and what stage of
boot we are at, and substitutions would have been done.

Fix by teaching env(8) to allow -L -/classname to set the class
environment with no pw entry at all specified, and use it in
service(8).

PR:		253959

2 files changed, 22 insertions, 10 deletions

diff --git a/usr.bin/env/env.1 b/usr.bin/env/env.1
index 8c0527608506..9aff9508e47b 100644
--- a/usr.bin/env/env.1
+++ b/usr.bin/env/env.1
@@ -31,7 +31,7 @@
 .\" From FreeBSD: src/usr.bin/printenv/printenv.1,v 1.17 2002/11/26 17:33:35 ru Exp
 .\" $FreeBSD$
 .\"
-.Dd November 11, 2020
+.Dd March 3, 2021
 .Dt ENV 1
 .Os
 .Sh NAME
@@ -104,6 +104,11 @@ is used, then the specified user's
 .Pa ~/.login_conf
 is read as well.
 The user may be specified by name or by uid.
+If a username of
+.Sq Li \&-
+is given, then no user lookup will be done, the login class will default to
+.Sq Li default
+if not explicitly given, and no substitutions will be done on the values.
 .\"	-P
 .It Fl P Ar altpath
 Search the set of directories as specified by
diff --git a/usr.bin/env/env.c b/usr.bin/env/env.c
index e408577ea7a4..0aa42a4663dd 100644
--- a/usr.bin/env/env.c
+++ b/usr.bin/env/env.c
@@ -144,16 +144,23 @@ main(int argc, char **argv)
 		login_class = strchr(login_name, '/');
 		if (login_class)
 			*login_class++ = '\0';
-		pw = getpwnam(login_name);
-		if (pw == NULL) {
-			char *endp = NULL;
-			errno = 0;
-			uid = strtoul(login_name, &endp, 10);
-			if (errno == 0 && *endp == '\0')
-				pw = getpwuid(uid);
+		if (*login_name != '\0' && strcmp(login_name,"-") != 0) {
+			pw = getpwnam(login_name);
+			if (pw == NULL) {
+				char *endp = NULL;
+				errno = 0;
+				uid = strtoul(login_name, &endp, 10);
+				if (errno == 0 && *endp == '\0')
+					pw = getpwuid(uid);
+			}
+			if (pw == NULL)
+				errx(EXIT_FAILURE, "no such user: %s", login_name);
 		}
-		if (pw == NULL)
-			errx(EXIT_FAILURE, "no such user: %s", login_name);
+		/*
+		 * Note that it is safe for pw to be null here; the libutil
+		 * code handles that, bypassing substitution of $ and using
+		 * the class "default" if no class name is given either.
+		 */
 		if (login_class != NULL) {
 			lc = login_getclass(login_class);
 			if (lc == NULL)