udhcpd: clamp down huge auto_times to ~2M seconds, better EINTR poll handling

EINTR _should_ only happen on two signals we trap, and safe_poll
_should_ work here just fine, but there were kernel bugs where spurious EINTRs
happen (e.g. on ptrace attach). Be safe.

function                                             old     new   delta
udhcpd_main                                         1437    1468     +31

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

1 files changed, 20 insertions, 5 deletions

diff --git a/networking/udhcp/dhcpd.c b/networking/udhcp/dhcpd.c
index db3ab4f00..19f94a2d7 100644
--- a/networking/udhcp/dhcpd.c
+++ b/networking/udhcp/dhcpd.c
@@ -853,6 +853,9 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
         /* Would rather not do read_config before daemonization -
          * otherwise NOMMU machines will parse config twice */
         read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE);
+        /* prevent poll timeout overflow */
+        if (server_config.auto_time > INT_MAX / 1000)
+                server_config.auto_time = INT_MAX / 1000;
 
         /* Make sure fd 0,1,2 are open */
         bb_sanitize_stdio();
@@ -914,14 +917,26 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
                 }
 
                 udhcp_sp_fd_set(pfds, server_socket);
-                tv = timeout_end - monotonic_sec();
-                /* Block here waiting for either signal or packet */
-                retval = safe_poll(pfds, 2, server_config.auto_time ? tv * 1000 : -1);
-                if (retval <= 0) {
-                        if (retval == 0) {
+
+ new_tv:
+                tv = -1;
+                if (server_config.auto_time) {
+                        tv = timeout_end - monotonic_sec();
+                        if (tv <= 0) {
+ write_leases:
                                 write_leases();
                                 goto continue_with_autotime;
                         }
+                        tv *= 1000;
+                }
+
+                /* Block here waiting for either signal or packet */
+                retval = poll(pfds, 2, tv);
+                if (retval <= 0) {
+                        if (retval == 0)
+                                goto write_leases;
+                        if (errno == EINTR)
+                                goto new_tv;
                         /* < 0 and not EINTR: should not happen */
                         bb_perror_msg_and_die("poll");
                 }