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>

diff --git a/networking/arping.c b/networking/arping.c
index 898c3054ea2232922a5a9d11775eae30cf054ad5..97e9e680a821ea6ab5836f562ef694a6182a00c8 100644 (file)
--- 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);
        }
 }