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

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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>
This commit is contained in:
Denys Vlasenko 2018-03-11 11:34:44 +01:00
parent 39dfb4de38
commit 3d306bffc5
1 changed files with 20 additions and 5 deletions
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25
networking/udhcp/dhcpd.c
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@ -853,6 +853,9 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
/* Would rather not do read_config before daemonization - /* Would rather not do read_config before daemonization -
* otherwise NOMMU machines will parse config twice */ * otherwise NOMMU machines will parse config twice */
read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE); 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 */ /* Make sure fd 0,1,2 are open */
bb_sanitize_stdio(); bb_sanitize_stdio();
@ -914,14 +917,26 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
} }
udhcp_sp_fd_set(pfds, server_socket); udhcp_sp_fd_set(pfds, server_socket);
tv = timeout_end - monotonic_sec();
/* Block here waiting for either signal or packet */ new_tv:
retval = safe_poll(pfds, 2, server_config.auto_time ? tv * 1000 : -1); tv = -1;
if (retval <= 0) { if (server_config.auto_time) {
if (retval == 0) { tv = timeout_end - monotonic_sec();
if (tv <= 0) {
write_leases:
write_leases(); write_leases();
goto continue_with_autotime; 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 */ /* < 0 and not EINTR: should not happen */
bb_perror_msg_and_die("poll"); bb_perror_msg_and_die("poll");
} }