don't mess up errno

1 files changed, 9 insertions, 2 deletions

diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index b3619fd0e..10ba9477c 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -27,9 +27,15 @@ unsigned short bb_lookup_port(const char *port, unsigned short default_port)
 {
         unsigned short port_nr = htons(default_port);
         if (port) {
-        char *endptr;
-                long port_long = strtol(port, &endptr, 10);
+                char *endptr;
+                int old_errno;
+                long port_long;
 
+                /* Since this is a lib function, we're not allowed to reset errno to 0.
+                 * Doing so could break an app that is deferring checking of errno. */
+                old_errno = errno;
+                errno = 0;
+                port_long = strtol(port, &endptr, 10);
                 if (errno != 0 || *endptr!='\0' || endptr==port || port_long < 0 || port_long > 65535) {
                         struct servent *tserv = getservbyname(port, "tcp");
                         if (tserv) {
@@ -38,6 +44,7 @@ unsigned short bb_lookup_port(const char *port, unsigned short default_port)
         } else {
                         port_nr = htons(port_long);
                 }
+                errno = old_errno;
         }
         return port_nr;
 }