telnetd: fix bad interaction with vhangup() from login

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

1 files changed, 16 insertions, 2 deletions

diff --git a/networking/telnetd.c b/networking/telnetd.c
index a6bafa21d..caef15181 100644
--- 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;