Support lockfiles in non-writable directories.

svn path=/branches/BRANCH_6-3/; revision=4946

3 files changed, 20 insertions, 2 deletions

diff --git a/NEWS b/NEWS
index 2e2fa467..41d23951 100644
--- a/NEWS
+++ b/NEWS
@@ -60,6 +60,8 @@ fetchmail 6.3.6 (not yet released):
   #9412, #9449. Stack backtrace provided by Neil Hoggarth - thanks.
 * Repair --logfile, broken in 6.3.5. BerliOS Bug #9059,
   reported by Brian Harring.
+* Robustness: If a stale lockfile cannot be deleted, truncate it to avoid
+  trouble later if the PID is recycled by a non-fetchmail process.
 
 # TRANSLATIONS:
 * New en_GB (British English) translation by David Lodge.
diff --git a/lock.c b/lock.c
index e56fe344..111559e7 100644
--- a/lock.c
+++ b/lock.c
@@ -91,12 +91,27 @@ int fm_lock_state(void)
 	fclose(lockfp); /* not checking should be safe, file mode was "r" */
 
 	if (args == EOF || args == 0 || kill(pid, 0) == -1) {
+	    /* ^ could not read PID  || process does not exist */
+	    /* => lockfile is stale, unlink it */
 	    pid = 0;
-
 	    fprintf(stderr,GT_("fetchmail: removing stale lockfile\n"));
 	    if (unlink(lockfile)) {
 	       if (errno != ENOENT) {
 		   perror(lockfile);
+		   /* we complain but we don't exit; it might be
+		    * writable for us, but in a directory we cannot
+		    * write to. This means we can write the new PID to
+		    * the file. Truncate to be safe in case the PID is
+		    * recycled by another process later.
+		    * \bug we should use fcntl() style locks or
+		    * something else instead in a future release. */
+		   if (truncate(lockfile, (off_t)0)) {
+		       /* but if we cannot truncate the file either,
+			* assume that we cannot write to it later,
+			* complain and quit. */
+		       perror(lockfile);
+		       exit(PS_EXCLUDE);
+		   }
 	       }
 	    }
 	}
diff --git a/lock.h b/lock.h
index 66b2c36f..27f63cf0 100644
--- a/lock.h
+++ b/lock.h
@@ -22,7 +22,8 @@ void fm_lock_release(void);
 
 /** Check the state of the lock file. If there is an error opening or
  * reading the lockfile, exit with PS_EXCLUDE. If a stale lock file
- * cannot be unlinked, complain, but continue.  \return
+ * cannot be unlinked, complain and try to truncate it to 0 size. If
+ * truncation fails, complain and exit with PS_EXCLUDE.  \return
  * -  0 if no lock is set
  * - >0 if a fetchmail is running, but not in daemon mode
  * - <0 if a fetchmail is running in daemon mode.