*: don't use getservbyname, it links in a static buffer

function                                             old     new   delta
bb_get_servport_by_name                                -     348    +348
bb_lookup_port                                        83     111     +28
reread_config_file                                   886     907     +21
static.se                                             16       -     -16
getservbyname                                         53       -     -53
getservbyname_r                                      284       -    -284
------------------------------------------------------------------------------
(add/remove: 2/5 grow/shrink: 2/0 up/down: 397/-353)           Total: 44 bytes
   text	   data	    bss	    dec	    hex	filename
1080084	    555	   5024	1085663	 1090df	busybox_old
1080144	    555	   4992	1085691	 1090fb	busybox_unstripped

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

5 files changed, 145 insertions, 37 deletions

diff --git a/include/libbb.h b/include/libbb.h
index e282066b8..0fee62929 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -911,9 +911,11 @@ char* xmalloc_sockaddr2hostonly_noport(const struct sockaddr *sa) FAST_FUNC RETU
 /* inet_[ap]ton on steroids */
 char* xmalloc_sockaddr2dotted(const struct sockaddr *sa) FAST_FUNC RETURNS_MALLOC;
 char* xmalloc_sockaddr2dotted_noport(const struct sockaddr *sa) FAST_FUNC RETURNS_MALLOC;
-// NB: unlike getservbyport, port parameter is NOT in network order
+// NB: unlike getservbyport, port parameter/retval are in host, NOT network order!
 #define getservbyport dont_use_getservbyport_uses_global_buffer
 char* bb_get_servname_by_port(char **p_etc_services, int port, const char *type) FAST_FUNC RETURNS_MALLOC;
+#define getservbyname dont_use_getservbyname_uses_global_buffer
+int bb_get_servport_by_name(char **p_etc_services, const char *name, const char *type) FAST_FUNC;
 // "old" (ipv4 only) API
 // users: traceroute.c hostname.c - use _list_ of all IPs
 struct hostent *xgethostbyname(const char *name) FAST_FUNC;
diff --git a/libbb/bb_get_servname_by_port.c b/libbb/bb_get_servname_by_port.c
index 3846072f9..970a718fe 100644
--- a/libbb/bb_get_servname_by_port.c
+++ b/libbb/bb_get_servname_by_port.c
@@ -9,11 +9,9 @@
 //kbuild:lib-$(CONFIG_PSCAN) += bb_get_servname_by_port.o
 #include "libbb.h"
 
-//Rationale for exising:
+//Rationale for existing:
 //#define getservbyport dont_use_getservbyport_uses_global_buffer
 //(for example: -280 bytes on musl, x86-32)
-//TODO:
-//avoid getservbyname() as well
 
 char* FAST_FUNC bb_get_servname_by_port(char **p_etc_services, int port, const char *type)
 {
@@ -45,7 +43,7 @@ char* FAST_FUNC bb_get_servname_by_port(char **p_etc_services, int port, const c
                         end = is_prefixed_with(end, type);
                         if (!end
                          || !(isspace(*end) || *end == '\0'
-                            || *end == '#') // glibc treats "http 80/tcp#COMMENT" as valid
+                            || *end == '#') // glibc treats "http 80/tcp#COMMENT" (no space!) as valid
                         ) {
                                 goto next;
                         }
diff --git a/libbb/bb_get_servport_by_name.c b/libbb/bb_get_servport_by_name.c
new file mode 100644
index 000000000..96580c900
--- /dev/null
+++ b/libbb/bb_get_servport_by_name.c
@@ -0,0 +1,129 @@
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2026 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//kbuild:lib-y += bb_get_servport_by_name.o
+//kbuild:lib-y += bb_get_servport_by_name.o
+#include "libbb.h"
+
+//Rationale for existing:
+//#define getservbyname dont_use_getservbyname_uses_global_buffer
+//(for example: -32 BSS bytes on musl, x86-32)
+
+int FAST_FUNC bb_get_servport_by_name(char **p_etc_services, const char *name, const char *proto)
+{
+        unsigned namelen;
+        char *sp;
+
+        if (!name[0]) // This can hang the search (strstr advances by 0 bytes)
+                return -1; // bad service name form: ""
+        // Any other bogosity to reject?
+        // Or just enforce isalnum_or_dash_or_slash(name[i])?
+        // Yes, service name like "cl/1" is allowed and _exists_.
+        //
+        // Protect against finding service "www#c" in "http 10/tcp www#c" line
+        //if (strchr(name, '#'))
+        //      return -1; // bad service name form
+        //^^^^ the main code already catches this possibility.
+        //
+        // Current code allows e.g. service names like "http 80/tcp"
+        // to map to port 80. Probably harmless?
+        //if (skip_non_whitespace(name)[0])
+        //      return -1; // bad service name form (has whitespace)
+
+        sp = *p_etc_services;
+        if (!sp) {
+//TODO: we need mmap_entire_file() for this use case!
+                sp = xmalloc_open_read_close("/etc/services", NULL);
+                if (!sp)
+                        return -1;
+                *p_etc_services = sp;
+        }
+        namelen = strlen(name);
+        while (*sp) {
+                const char *pnstr;
+                char *start, *end;
+                unsigned n;
+
+                // First, find a possible service name without regard for line separators (!)
+                start = strstr(sp, name);
+                if (!start)
+                        return -1;
+                sp = start + namelen;
+                if (start != *p_etc_services && !isspace(start[-1])) {
+                        // There is a char before it, and it's not whitespace
+                        continue;
+                }
+                if (!(isspace(*sp) || *sp == '\0' || *sp == '#'))
+                        // After it: not whitespace/EOF/comment
+                        continue;
+                // The found substring _is_ correctly delimited before and after
+
+                // Find beginning of the line we are on
+                while (start != *p_etc_services && start[-1] != '\n')
+                        start--;
+                start = skip_whitespace(start);
+                // Is there a comment char between start of line and "service name"?
+                if (memchr(start, '#', sp - start)) {
+                        // The "service name" we found is actually in comment / has comment in it.
+                        // Also rejects names with #:
+                        // service "www#c" won't be found even on "http 80/tcp www#c" line
+                        continue;
+                }
+                // Is the [start...sp) of the form "SERVNAME NUM/PROTO[ ALIAS[ ALIAS...][ ]]"?
+                pnstr = skip_whitespace(skip_non_whitespace(start)); // go to NUM...
+
+                // I've seen this line in /etc/services of a real-world machine:
+                //914c/g 211/tcp 914c-g
+                // Now consider just a bit more pathological example:
+                //914c/tcp 914/tcp 914/tcp
+                // If we search for service name "914/tcp",
+                // we'll find it at second word first, yet we must not reject this line
+                // because the THIRD word also matches, and it's a valid match (tested on glibc!).
+                // But in this case we must not match:
+                //914c/tcp 914/tcp something-else
+                if (sp - namelen == pnstr)
+                        continue; // the match is at NUM..., try matching further
+
+                n = bb_strtou(pnstr, &end, 10);
+                if (n > 0xffff || *end != '/')
+                        continue; // NUM... part is not a valid port#, or has no slash
+
+                if (proto) {
+                        end++; // points to PROTO
+                        end = is_prefixed_with(end, proto);
+                        if (!end
+                         || !(isspace(*end) || *end == '\0'
+                            || *end == '#') // glibc treats "http 80/tcp#COMMENT" (no space!) as valid
+                        ) {
+                                continue; // PROTO does not match
+                        }
+                }
+                // By now, either WORD or one of the ALIASes has to be the part
+                // which was found by strstr()!
+                return n;
+        }
+        return -1;
+}
+
+// Return port number for a service.
+// If "port" is a number use it as the port.
+// If "port" is a name it is looked up in /etc/services.
+// if NULL, return default_port
+unsigned FAST_FUNC bb_lookup_port(const char *port, const char *protocol, unsigned port_nr)
+{
+        if (port) {
+                port_nr = bb_strtou(port, NULL, 10);
+                if (errno || port_nr > 65535) {
+                        char *p_etc_services = NULL;
+                        port_nr = bb_get_servport_by_name(&p_etc_services, port, protocol);
+                        if (port_nr > 0xffff) // -1?
+                                bb_error_msg_and_die("bad port '%s'", port);
+                        free(p_etc_services);
+                }
+        }
+        return (uint16_t)port_nr;
+}
diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index 0e0b247b8..095f7ff47 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -113,29 +113,8 @@ void FAST_FUNC xconnect(int s, const struct sockaddr *s_addr, socklen_t addrlen)
         }
 }
 
-/* Return port number for a service.
- * If "port" is a number use it as the port.
- * If "port" is a name it is looked up in /etc/services.
- * if NULL, return default_port
- */
-unsigned FAST_FUNC bb_lookup_port(const char *port, const char *protocol, unsigned port_nr)
-{
-        if (port) {
-                port_nr = bb_strtou(port, NULL, 10);
-                if (errno || port_nr > 65535) {
-                        struct servent *tserv = getservbyname(port, protocol);
-                        if (!tserv)
-                                bb_error_msg_and_die("bad port '%s'", port);
-                        port_nr = ntohs(tserv->s_port);
-                }
-        }
-        return (uint16_t)port_nr;
-}
-
-
 /* "New" networking API */
 
-
 int FAST_FUNC get_nport(const struct sockaddr *sa)
 {
 #if ENABLE_FEATURE_IPV6
diff --git a/networking/inetd.c b/networking/inetd.c
index e63edcd9d..6220a08e3 100644
--- a/networking/inetd.c
+++ b/networking/inetd.c
@@ -969,9 +969,8 @@ static void reread_config_file(int sig UNUSED_PARAM)
         servtab_t *sep, *cp, **sepp;
         len_and_sockaddr *lsa;
         sigset_t omask;
-        unsigned n;
-        uint16_t port;
         int save_errno = errno;
+        char *p_etc_services = NULL;
 
         if (!reopen_config_file())
                 goto ret;
@@ -1039,7 +1038,9 @@ static void reread_config_file(int sig UNUSED_PARAM)
                         break;
 
                 default: /* case AF_INET, case AF_INET6 */
-                        n = bb_strtou(sep->se_service, NULL, 10);
+                {
+                        unsigned portno;
+                        portno = bb_strtou(sep->se_service, NULL, 10);
 #if ENABLE_FEATURE_INETD_RPC
                         if (is_rpc_service(sep)) {
                                 sep->se_rpcprog = n;
@@ -1059,26 +1060,23 @@ static void reread_config_file(int sig UNUSED_PARAM)
                         }
 #endif
                         /* what port to listen on? */
-                        port = htons(n);
-                        if (errno || n > 0xffff) { /* se_service is not numeric */
+                        if (errno || portno > 0xffff) { /* se_service is not numeric */
                                 char protoname[4];
-                                struct servent *sp;
                                 /* can result only in "tcp" or "udp": */
                                 safe_strncpy(protoname, sep->se_proto, 4);
-                                sp = getservbyname(sep->se_service, protoname);
-                                if (sp == NULL) {
+                                portno = bb_get_servport_by_name(&p_etc_services, sep->se_service, protoname);
+                                if (portno > 0xffff) {
                                         bb_error_msg("%s/%s: unknown service",
                                                         sep->se_service, sep->se_proto);
                                         goto next_cp;
                                 }
-                                port = sp->s_port;
                         }
                         if (LONE_CHAR(sep->se_local_hostname, '*')) {
                                 lsa = xzalloc_lsa(sep->se_family);
-                                set_nport(&lsa->u.sa, port);
+                                set_nport(&lsa->u.sa, htons(portno));
                         } else {
                                 lsa = host_and_af2sockaddr(sep->se_local_hostname,
-                                                ntohs(port), sep->se_family);
+                                                portno, sep->se_family);
                                 if (!lsa) {
                                         bb_error_msg("%s/%s: unknown host '%s'",
                                                 sep->se_service, sep->se_proto,
@@ -1087,6 +1085,7 @@ static void reread_config_file(int sig UNUSED_PARAM)
                                 }
                         }
                         break;
+                }//default:
                 } /* end of "switch (sep->se_family)" */
 
                 /* did lsa change? Then close/open */
@@ -1134,6 +1133,7 @@ static void reread_config_file(int sig UNUSED_PARAM)
         }
         restore_sigmask(&omask);
  ret:
+        free(p_etc_services);
         errno = save_errno;
 }