Attachment 36417 Details for Bug 63140 – Avoids pid file creation race condition by using a temporary file.

[patch] Avoids pid file creation race condition by using a temporary file.

0001-apache-atomic-creation-of-pid-file.patch (text/plain), 2.75 KB, created by Nicolas Carrier on 2019-02-04 11:00:58 UTC

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Creator: Nicolas Carrier

Created: 2019-02-04 11:00:58 UTC

Size: 2.75 KB

patch

obsolete

>From b50dfff90756a92d033d4acf0717796953236334 Mon Sep 17 00:00:00 2001
>From: Nicolas Carrier <nicolas.carrier@orolia.com>
>Date: Mon, 4 Feb 2019 11:49:19 +0100
>Subject: apache: atomic creation of pid file.
>
>The original pattern for creating the pid file was:
>open_create(pid_file)
>write(pid_file, pid)
>close(pid_file)
>
>But if a power outage occurs between open_create and write, the file will
>be empty and httpd will refuse to start afterwards unless the corrupt pid
>file is removed.
>
>This patch uses the pattern:
>open_create(temp_pid_file)
>write(temp_pid_file)
>close(temp_pid_file)
>rename(temp_pid_file, pid_file)
>which is guaranteed to be atomic, provided that temp_pid_file and pid_file
>are located in the same file system, which this patch does by creating
>a temporary file name with the pattern:
>    pid_file_name + random_suffix
>---
> server/log.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
>diff --git a/server/log.c b/server/log.c
>index 3763e8b1fc..cedfbe71bc 100644
>--- a/server/log.c
>+++ b/server/log.c
>@@ -1524,6 +1524,8 @@ AP_DECLARE(void) ap_log_pid(apr_pool_t *p, const char *filename)
>     pid_t mypid;
>     apr_status_t rv;
>     const char *fname;
>+    char *temp_fname;
>+    apr_fileperms_t perms;
> 
>     if (!filename) {
>         return;
>@@ -1535,6 +1537,10 @@ AP_DECLARE(void) ap_log_pid(apr_pool_t *p, const char *filename)
>                      ap_server_conf, APLOGNO(00097) "Invalid PID file path %s, ignoring.", filename);
>         return;
>     }
>+    temp_fname = apr_psprintf(p, "%s.XXXXXX", filename);
>+    if (!temp_fname) {
>+        return;
>+    }
> 
>     mypid = getpid();
>     if (mypid != saved_pid
>@@ -1552,19 +1558,23 @@ AP_DECLARE(void) ap_log_pid(apr_pool_t *p, const char *filename)
>                       fname);
>     }
> 
>-    if ((rv = apr_file_open(&pid_file, fname,
>-                            APR_WRITE | APR_CREATE | APR_TRUNCATE,
>-                            APR_UREAD | APR_UWRITE | APR_GREAD | APR_WREAD, p))
>+    if ((rv = apr_file_mktemp(&pid_file, temp_fname,
>+                              APR_WRITE | APR_CREATE | APR_TRUNCATE, p))
>         != APR_SUCCESS) {
>         ap_log_error(APLOG_MARK, APLOG_ERR, rv, NULL, APLOGNO(00099)
>-                     "could not create %s", fname);
>+                     "could not create %s", temp_fname);
>         ap_log_error(APLOG_MARK, APLOG_ERR, 0, NULL, APLOGNO(00100)
>                      "%s: could not log pid to file %s",
>                      ap_server_argv0, fname);
>         exit(1);
>     }
>+
>+    perms = APR_UREAD | APR_UWRITE | APR_GREAD | APR_WREAD;
>+    apr_file_perms_set(temp_fname, perms);
>+
>     apr_file_printf(pid_file, "%" APR_PID_T_FMT APR_EOL_STR, mypid);
>     apr_file_close(pid_file);
>+    apr_file_rename(temp_fname, fname, p);
>     saved_pid = mypid;
> }
> 
>-- 
>2.11.0
>

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Attachments on bug 63140: 36417