MDEV-9383: Server fails to read master.info after upgrade 10.0 -> 10.1

In some cases, MariaDB 10.0 could write a master.info file that was read
incorrectly by 10.1 and could cause server to fail to start after an upgrade.

(If writing a new master.info file that is shorter than the old, extra
junk may remain at the end of the file. This is handled properly in
10.1 with an END_MARKER line, but this line is not written by
10.0. The fix here is to make 10.1 robust at reading the master.info
files written by 10.0).

Fix several things around reading master.info and read_mi_key_from_file():

 - read_mi_key_from_file() did not distinguish between a line with and
   without an eqals '=' sign.

 - If a line was empty, read_mi_key_from_file() would incorrectly return
   the key from the previous call.

 - An extra using_gtid=X line left-over by MariaDB 10.0 might incorrectly
   be read and overwrite the correct value.

 - Fix incorrect usage of strncmp() which should be strcmp().

 - Add test cases.

1 files changed, 48 insertions, 33 deletions

diff --git a/sql/rpl_mi.cc b/sql/rpl_mi.cc
index df721342d1d..02dbac46eb5 100644
--- a/sql/rpl_mi.cc
+++ b/sql/rpl_mi.cc
@@ -205,43 +205,56 @@ void init_master_log_pos(Master_info* mi)
 
 /**
   Parses the IO_CACHE for "key=" and returns the "key".
+  If no '=' found, returns the whole line (for END_MARKER).
 
   @param key      [OUT]               Key buffer
   @param max_size [IN]                Maximum buffer size
   @param f        [IN]                IO_CACHE file
+  @param found_equal [OUT]            Set true if a '=' was found.
 
   @retval 0                           Either "key=" or '\n' found
   @retval 1                           EOF
 */
-static int read_mi_key_from_file(char *key, int max_size, IO_CACHE *f)
+static int
+read_mi_key_from_file(char *key, int max_size, IO_CACHE *f, bool *found_equal)
 {
   int i= 0, c;
-  char *last_p;
 
   DBUG_ENTER("read_key_from_file");
 
-  while (((c= my_b_get(f)) != '\n') && (c != my_b_EOF))
+  *found_equal= false;
+  if (max_size <= 0)
+    DBUG_RETURN(1);
+  for (;;)
   {
-    last_p= key + i;
-
-    if (i < max_size)
+    if (i >= max_size-1)
     {
-      if (c == '=')
-      {
-        /* We found '=', replace it by 0 and return. */
-        *last_p= 0;
-        DBUG_RETURN(0);
-      }
-      else
-        *last_p= c;
+      key[i] = '\0';
+      DBUG_RETURN(0);
+    }
+    c= my_b_get(f);
+    if (c == my_b_EOF)
+    {
+      DBUG_RETURN(1);
+    }
+    else if (c == '\n')
+    {
+      key[i]= '\0';
+      DBUG_RETURN(0);
+    }
+    else if (c == '=')
+    {
+      key[i]= '\0';
+      *found_equal= true;
+      DBUG_RETURN(0);
+    }
+    else
+    {
+      key[i]= c;
+      ++i;
     }
-    ++i;
   }
-
-  if (c == my_b_EOF)
-    DBUG_RETURN(1);
-
-  DBUG_RETURN(0);
+  /* NotReached */
 }
 
 enum {
@@ -539,6 +552,10 @@ file '%s')", fname);
       if (lines >= LINE_FOR_LAST_MYSQL_FUTURE)
       {
         uint i;
+        bool got_eq;
+        bool seen_using_gtid= false;
+        bool seen_do_domain_ids=false, seen_ignore_domain_ids=false;
+
         /* Skip lines used by / reserved for MySQL >= 5.6. */
         for (i= LINE_FOR_FIRST_MYSQL_5_6; i <= LINE_FOR_LAST_MYSQL_FUTURE; ++i)
         {
@@ -551,11 +568,12 @@ file '%s')", fname);
           for "key=" and returns the "key" if found. The "value" can then the
           parsed on case by case basis. The "unknown" lines would be ignored to
           facilitate downgrades.
+          10.0 does not have the END_MARKER before any left-overs at the end
+          of the file. So ignore any but the first occurrence of a key.
         */
-        while (!read_mi_key_from_file(buf, sizeof(buf), &mi->file))
+        while (!read_mi_key_from_file(buf, sizeof(buf), &mi->file, &got_eq))
         {
-          /* using_gtid */
-          if (!strncmp(buf, STRING_WITH_LEN("using_gtid")))
+          if (got_eq && !seen_using_gtid && !strcmp(buf, "using_gtid"))
           {
             int val;
             if (!init_intvar_from_file(&val, &mi->file, 0))
@@ -566,15 +584,13 @@ file '%s')", fname);
                 mi->using_gtid= Master_info::USE_GTID_SLAVE_POS;
               else
                 mi->using_gtid= Master_info::USE_GTID_NO;
-              continue;
+              seen_using_gtid= true;
             } else {
               sql_print_error("Failed to initialize master info using_gtid");
               goto errwithmsg;
             }
           }
-
-          /* DO_DOMAIN_IDS */
-          if (!strncmp(buf, STRING_WITH_LEN("do_domain_ids")))
+          else if (got_eq && !seen_do_domain_ids && !strcmp(buf, "do_domain_ids"))
           {
             if (mi->domain_id_filter.init_ids(&mi->file,
                                               Domain_id_filter::DO_DOMAIN_IDS))
@@ -582,11 +598,10 @@ file '%s')", fname);
               sql_print_error("Failed to initialize master info do_domain_ids");
               goto errwithmsg;
             }
-            continue;
+            seen_do_domain_ids= true;
           }
-
-          /* IGNORE_DOMAIN_IDS */
-          if (!strncmp(buf, STRING_WITH_LEN("ignore_domain_ids")))
+          else if (got_eq && !seen_ignore_domain_ids &&
+                   !strcmp(buf, "ignore_domain_ids"))
           {
             if (mi->domain_id_filter.init_ids(&mi->file,
                                               Domain_id_filter::IGNORE_DOMAIN_IDS))
@@ -595,9 +610,9 @@ file '%s')", fname);
                               "ignore_domain_ids");
               goto errwithmsg;
             }
-            continue;
+            seen_ignore_domain_ids= true;
           }
-          else if (!strncmp(buf, STRING_WITH_LEN("END_MARKER")))
+          else if (!got_eq && !strcmp(buf, "END_MARKER"))
           {
             /*
               Guard agaist extra left-overs at the end of file, in case a later