From: Pádraig Brady <P@draigBrady.com>
Date: Tue, 28 Feb 2023 13:34:31 +0000 (+0000)
Subject: tail: avoid undefined behavior when polling outputs
X-Git-Tag: v9.2~40
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5bcc2912e7d7c16d3052a7ed4f0904f72573255e;p=thirdparty%2Fcoreutils.git

tail: avoid undefined behavior when polling outputs

* src/tail.c (check_output_alive): Only check the returned
events from poll() when it indicates there are events to check.
---

diff --git a/src/tail.c b/src/tail.c
index e2e7f46909..78022fc4b5 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -367,9 +367,9 @@ check_output_alive (void)
   struct pollfd pfd;
   pfd.fd = STDOUT_FILENO;
   pfd.events = pfd.revents = 0;
-  pfd.events |= POLLRDBAND; /* Needed for illumos, macos.  */
+  pfd.events |= POLLRDBAND; /* Needed for illumos, macOS.  */
 
-  if (poll (&pfd, 1, 0) >= 0 && (pfd.revents & (POLLERR | POLLHUP)))
+  if (poll (&pfd, 1, 0) > 0 && (pfd.revents & (POLLERR | POLLHUP)))
     die_pipe ();
 #else
   struct timeval delay;