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From c7a04cef4075da864a3468e63a5bb79334d8f556 Mon Sep 17 00:00:00 2001
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From: Paul Eggert <eggert@cs.ucla.edu>
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Date: Sat, 26 Jun 2021 18:23:52 -0700
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Subject: [PATCH] tail: use poll, not select
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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This fixes an unlikely stack out-of-bounds write reported by
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Stepan Broz via Kamil Dudka (Bug#49209).
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* src/tail.c: Do not include <sys/select.h>.
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[!_AIX]: Include poll.h.
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(check_output_alive) [!_AIX]: Use poll instead of select.
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(tail_forever_inotify): Likewise. Simplify logic, as there is no
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need for a ‘while (len <= evbuf_off)’ loop.
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Upstream-commit: da0d448bca62c6305fc432f67e2c5ccc2da75346
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Signed-off-by: Kamil Dudka <kdudka@redhat.com>
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---
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src/tail.c | 100 +++++++++++++++++++++--------------------------------
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1 file changed, 39 insertions(+), 61 deletions(-)
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diff --git a/src/tail.c b/src/tail.c
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index 1c88723..5b4f21a 100644
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--- a/src/tail.c
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+++ b/src/tail.c
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@@ -28,12 +28,9 @@
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#include <stdio.h>
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#include <assert.h>
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#include <getopt.h>
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-#include <sys/select.h>
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+#include <poll.h>
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#include <sys/types.h>
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#include <signal.h>
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-#ifdef _AIX
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-# include <poll.h>
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-#endif
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#include "system.h"
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#include "argmatch.h"
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@@ -351,27 +348,12 @@ check_output_alive (void)
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if (! monitor_output)
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return;
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-#ifdef _AIX
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- /* select on AIX was seen to give a readable event immediately. */
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struct pollfd pfd;
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pfd.fd = STDOUT_FILENO;
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pfd.events = POLLERR;
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if (poll (&pfd, 1, 0) >= 0 && (pfd.revents & POLLERR))
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die_pipe ();
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-#else
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- struct timeval delay;
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- delay.tv_sec = delay.tv_usec = 0;
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-
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- fd_set rfd;
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- FD_ZERO (&rfd);
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- FD_SET (STDOUT_FILENO, &rfd);
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-
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- /* readable event on STDOUT is equivalent to POLLERR,
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- and implies an error condition on output like broken pipe. */
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- if (select (STDOUT_FILENO + 1, &rfd, NULL, NULL, &delay) == 1)
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- die_pipe ();
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-#endif
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}
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static bool
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@@ -1612,7 +1594,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
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/* Wait for inotify events and handle them. Events on directories
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ensure that watched files can be re-added when following by name.
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This loop blocks on the 'safe_read' call until a new event is notified.
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- But when --pid=P is specified, tail usually waits via the select. */
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+ But when --pid=P is specified, tail usually waits via poll. */
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while (1)
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{
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struct File_spec *fspec;
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@@ -1629,54 +1611,51 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
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return false;
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}
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- /* When watching a PID, ensure that a read from WD will not block
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- indefinitely. */
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- while (len <= evbuf_off)
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+ if (len <= evbuf_off)
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{
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- struct timeval delay; /* how long to wait for file changes. */
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+ /* Poll for inotify events. When watching a PID, ensure
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+ that a read from WD will not block indefinitely.
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+ If MONITOR_OUTPUT, also poll for a broken output pipe. */
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- if (pid)
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+ int file_change;
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+ struct pollfd pfd[2];
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+ do
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{
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- if (writer_is_dead)
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- exit (EXIT_SUCCESS);
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+ /* How many ms to wait for changes. -1 means wait forever. */
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+ int delay = -1;
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- writer_is_dead = (kill (pid, 0) != 0 && errno != EPERM);
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-
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- if (writer_is_dead)
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- delay.tv_sec = delay.tv_usec = 0;
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- else
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+ if (pid)
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{
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- delay.tv_sec = (time_t) sleep_interval;
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- delay.tv_usec = 1000000 * (sleep_interval - delay.tv_sec);
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+ if (writer_is_dead)
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+ exit (EXIT_SUCCESS);
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+
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+ writer_is_dead = (kill (pid, 0) != 0 && errno != EPERM);
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+
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+ if (writer_is_dead || sleep_interval <= 0)
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+ delay = 0;
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+ else if (sleep_interval < INT_MAX / 1000 - 1)
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+ {
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+ /* delay = ceil (sleep_interval * 1000), sans libm. */
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+ double ddelay = sleep_interval * 1000;
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+ delay = ddelay;
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+ delay += delay < ddelay;
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+ }
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}
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+
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+ pfd[0].fd = wd;
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+ pfd[0].events = POLLIN;
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+ pfd[1].fd = STDOUT_FILENO;
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+ pfd[1].events = pfd[1].revents = 0;
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+ file_change = poll (pfd, monitor_output + 1, delay);
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}
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+ while (file_change == 0);
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- fd_set rfd;
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- FD_ZERO (&rfd);
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- FD_SET (wd, &rfd);
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- if (monitor_output)
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- FD_SET (STDOUT_FILENO, &rfd);
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-
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- int file_change = select (MAX (wd, STDOUT_FILENO) + 1,
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- &rfd, NULL, NULL, pid ? &delay: NULL);
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-
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- if (file_change == 0)
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- continue;
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- else if (file_change == -1)
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- die (EXIT_FAILURE, errno,
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- _("error waiting for inotify and output events"));
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- else if (FD_ISSET (STDOUT_FILENO, &rfd))
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- {
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- /* readable event on STDOUT is equivalent to POLLERR,
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- and implies an error on output like broken pipe. */
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- die_pipe ();
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- }
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- else
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- break;
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- }
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+ if (file_change < 0)
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+ die (EXIT_FAILURE, errno,
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+ _("error waiting for inotify and output events"));
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+ if (pfd[1].revents)
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+ die_pipe ();
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- if (len <= evbuf_off)
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- {
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len = safe_read (wd, evbuf, evlen);
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evbuf_off = 0;
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@@ -2437,8 +2416,7 @@ main (int argc, char **argv)
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if (forever && ignore_fifo_and_pipe (F, n_files))
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{
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/* If stdout is a fifo or pipe, then monitor it
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- so that we exit if the reader goes away.
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- Note select() on a regular file is always readable. */
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+ so that we exit if the reader goes away. */
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struct stat out_stat;
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if (fstat (STDOUT_FILENO, &out_stat) < 0)
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die (EXIT_FAILURE, errno, _("standard output"));
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--
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2.31.1
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