[PATCH] linux: always update select timeout (bug 27706)

[Andreas Schwab <schwab@suse.de>]

When select returns, sucessfully or not, the timeout argument should
always be updated with the remaining timeout value.  Due to a use of the
wrong function for conversion, that never happend for configurations that
support 64-bit time_t.  For other configurations, the timeout was only
updated on sucessful return.
---
 sysdeps/unix/sysv/linux/Makefile              |  2 +-
 sysdeps/unix/sysv/linux/select.c              |  6 +-
 .../sysv/linux/tst-select-update-timeout.c    | 55 +++++++++++++++++++
 3 files changed, 59 insertions(+), 4 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/tst-select-update-timeout.c

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 303fa297bc..e8524e0483 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -109,7 +109,7 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
 	 tst-tgkill tst-sysvsem-linux tst-sysvmsg-linux tst-sysvshm-linux \
 	 tst-timerfd tst-ppoll tst-futimens tst-utime tst-utimes \
 	 tst-clock_adjtime tst-adjtimex tst-ntp_adjtime tst-ntp_gettime \
-	 tst-ntp_gettimex tst-sigtimedwait
+	 tst-ntp_gettimex tst-sigtimedwait tst-select-update-timeout
 
 # Test for the symbol version of fcntl that was replaced in glibc 2.28.
 ifeq ($(have-GLIBC_2.27)$(build-shared),yesyes)
diff --git a/sysdeps/unix/sysv/linux/select.c b/sysdeps/unix/sysv/linux/select.c
index 415aa87d3c..ad3e0ec634 100644
--- a/sysdeps/unix/sysv/linux/select.c
+++ b/sysdeps/unix/sysv/linux/select.c
@@ -55,7 +55,7 @@ __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
       if (r == 0 || errno != ENOSYS)
 	{
 	  if (timeout != NULL)
-	    TIMEVAL_TO_TIMESPEC (timeout, &ts64);
+	    TIMESPEC_TO_TIMEVAL (timeout, &ts64);
 	  return r;
 	}
 
@@ -84,7 +84,7 @@ __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
   r = SYSCALL_CANCEL (pselect6, nfds, readfds, writefds, exceptfds, pts32,
 		      NULL);
 # endif
-  if (r >= 0 && timeout != NULL)
+  if (timeout != NULL)
     *timeout = valid_timespec_to_timeval64 (ts32);
 #endif
 
@@ -105,7 +105,7 @@ __select (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
       ptv64 = &tv64;
     }
   int r = __select64 (nfds, readfds, writefds, exceptfds, ptv64);
-  if (r >= 0 && timeout != NULL)
+  if (timeout != NULL)
     /* The remanining timeout will be always less the input TIMEOUT.  */
     *timeout = valid_timeval64_to_timeval (tv64);
   return r;
diff --git a/sysdeps/unix/sysv/linux/tst-select-update-timeout.c b/sysdeps/unix/sysv/linux/tst-select-update-timeout.c
new file mode 100644
index 0000000000..454d4e3ada
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-select-update-timeout.c
@@ -0,0 +1,55 @@
+/* Test for select timeout updated after return.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sys/select.h>
+#include <errno.h>
+#include <unistd.h>
+#include <support/check.h>
+#include <support/xsignal.h>
+
+static void
+alarm_handler (int signum)
+{
+  /* Do nothing.  */
+}
+
+static int
+do_test (void)
+{
+  /* When select returns, successfully or not, the timeout argument should
+     be updated with the remaining timeout value.  */
+
+  struct timeval tv = { .tv_sec = 1 };
+  int r = select (0, NULL, NULL, NULL, &tv);
+  TEST_COMPARE (r, 0);
+  TEST_COMPARE (tv.tv_sec, 0);
+
+  struct sigaction act = { .sa_handler = alarm_handler };
+  xsigaction (SIGALRM, &act, NULL);
+  alarm (2);
+
+  tv.tv_sec = 10;
+  r = select (0, NULL, NULL, NULL, &tv);
+  TEST_COMPARE (r, -1);
+  TEST_COMPARE (errno, EINTR);
+  TEST_VERIFY (tv.tv_sec < 10);
+
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.31.1


-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."