Avoid dangling-pointer usage in pg_basebackup progress reports.

Ill-considered refactoring in 23a1c6578 led to progress_filename
sometimes pointing to data that had gone out of scope.  The most
bulletproof fix is to hang onto a copy of whatever's passed in.
Compared to the work spent elsewhere per file, that's not very
expensive, plus we can skip it except in verbose logging mode.

Per buildfarm.

Discussion: https://postgr.es/m/20220212211316.GK31460@telsasoft.com

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index 0003b59615753a88309330d48bb2f27f669b2bd6..08b07d5a06e90a79672dc165da8fb51a2531311e 100644 (file)
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -164,7 +164,7 @@ static bool found_tablespace_dirs = false;
 static uint64 totalsize_kb;
 static uint64 totaldone;
 static int tablespacecount;
-static const char *progress_filename;
+static char *progress_filename = NULL;
 
 /* Pipe to communicate with background wal receiver process */
 #ifndef WIN32
@@ -775,11 +775,22 @@ verify_dir_is_empty_or_create(char *dirname, bool *created, bool *found)
 
 /*
  * Callback to update our notion of the current filename.
+ *
+ * No other code should modify progress_filename!
  */
 static void
 progress_update_filename(const char *filename)
 {
-   progress_filename = filename;
+   /* We needn't maintain this variable if not doing verbose reports. */
+   if (showprogress && verbose)
+   {
+       if (progress_filename)
+           free(progress_filename);
+       if (filename)
+           progress_filename = pg_strdup(filename);
+       else
+           progress_filename = NULL;
+   }
 }
 
 /*
@@ -1258,7 +1269,7 @@ CreateBackupStreamer(char *archive_name, char *spclocation,
         */
        if (must_parse_archive)
            streamer = bbstreamer_tar_archiver_new(streamer);
-       progress_filename = archive_filename;
+       progress_update_filename(archive_filename);
    }
 
    /*
@@ -1662,7 +1673,7 @@ ReceiveTarFile(PGconn *conn, char *archive_name, char *spclocation,
                                          expect_unterminated_tarfile);
    state.tablespacenum = tablespacenum;
    ReceiveCopyData(conn, ReceiveTarCopyChunk, &state);
-   progress_filename = NULL;
+   progress_update_filename(NULL);
 
    /*
     * The decision as to whether we need to inject the backup manifest into
@@ -2161,7 +2172,7 @@ BaseBackup(void)
 
    if (showprogress)
    {
-       progress_filename = NULL;
+       progress_update_filename(NULL);
        progress_report(PQntuples(res), true, true);
    }