arping: fix the case when inherited signal mask masks out ALRM

function                                             old     new   delta
arping_main                                         1629    1635      +6

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

1 files changed, 16 insertions, 7 deletions

diff --git a/networking/arping.c b/networking/arping.c
index 898c3054e..97e9e680a 100644
--- a/networking/arping.c
+++ b/networking/arping.c
@@ -413,28 +413,37 @@ int arping_main(int argc UNUSED_PARAM, char **argv)
                 printf(" from %s %s\n", inet_ntoa(src), device);
         }
 
+        packet = xmalloc(4096);
+
         signal_SA_RESTART_empty_mask(SIGINT,  (void (*)(int))finish);
         signal_SA_RESTART_empty_mask(SIGALRM, (void (*)(int))catcher);
 
+        /* Send the first packet, arm ALRM */
         catcher();
 
-        packet = xmalloc(4096);
         while (1) {
-                sigset_t sset, osset;
+                sigset_t sset;
                 struct sockaddr_ll from;
                 socklen_t alen = sizeof(from);
                 int cc;
 
+                sigemptyset(&sset);
+                sigaddset(&sset, SIGALRM);
+                sigaddset(&sset, SIGINT);
+                /* Unblock SIGALRM so that the previously called alarm()
+                 * can prevent recvfrom from blocking forever in case the
+                 * inherited procmask is blocking SIGALRM.
+                 */
+                sigprocmask(SIG_UNBLOCK, &sset, NULL);
+
                 cc = recvfrom(sock_fd, packet, 4096, 0, (struct sockaddr *) &from, &alen);
+
+                /* Don't allow SIGALRMs while we process the reply */
+                sigprocmask(SIG_BLOCK, &sset, NULL);
                 if (cc < 0) {
                         bb_perror_msg("recvfrom");
                         continue;
                 }
-                sigemptyset(&sset);
-                sigaddset(&sset, SIGALRM);
-                sigaddset(&sset, SIGINT);
-                sigprocmask(SIG_BLOCK, &sset, &osset);
                 recv_pack(packet, cc, &from);
-                sigprocmask(SIG_SETMASK, &osset, NULL);
         }
 }