telnetd: fix bad interaction with vhangup() from login

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

diff --git a/networking/telnetd.c b/networking/telnetd.c
index a6bafa21df646536c4264b1d32b9a848513e6fd6..caef151811c846058249a0edeab9a24b609ed2ad 100644 (file)
--- a/networking/telnetd.c
+++ b/networking/telnetd.c
@@ -865,11 +865,25 @@ int telnetd_main(int argc UNUSED_PARAM, char **argv)
  skip3:
                if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
                        /* Read from pty to buffer 2 */
+                       int eio = 0;
+ read_pty:
                        count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
                        count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
                        if (count <= 0) {
-                               if (count < 0 && errno == EAGAIN)
-                                       goto skip4;
+                               if (count < 0) {
+                                       if (errno == EAGAIN)
+                                               goto skip4;
+                                       /* login process might call vhangup(),
+                                        * which causes intermittent EIOs on read above
+                                        * (observed on kernel 4.12.0). Try up to 10 ms.
+                                        */
+                                       if (errno == EIO && eio < 10) {
+                                               eio++;
+                                               //bb_error_msg("EIO pty %u", eio);
+                                               usleep(1000);
+                                               goto read_pty;
+                                       }
+                               }
                                goto kill_session;
                        }
                        ts->size2 += count;