Bug#17583: mysql drops connection when stdout is not writable

When the client program had its stdout file descriptor closed by the calling
shell, after some amount of work (enough to fill a socket buffer) the server 
would complain about a packet error and then disconnect the client.

This is a serious security problem.  If stdout is closed before the mysql is
exec()d, then the first socket() call allocates file number 1 to communicate
with the server.  Subsequent write()s to that file number (as when printing
results that come back from the database) go back to the server instead in 
the command channel.  So, one should be able to craft data which, upon being
selected back from the server to the client, and injected into the command
stream become valid MySQL protocol to do something nasty when sent /back/ to 
the server.

The solution is to close explicitly the file descriptor that we *printf() to, 
so that the libc layer and the OS layer both agree that the file is closed.

BitKeeper/etc/collapsed

+452a92d0-31-8wSzSfZi165fcGcXPA

client/mysql.cc

@@ -372,6 +372,21 @@ int main(int argc,char *argv[])
   else
     status.add_to_history=1;
   status.exit_status=1;
+
+  {
+    /* 
+     The file descriptor-layer may be out-of-sync with the file-number layer,
+     so we make sure that "stdout" is really open.  If its file is closed then
+     explicitly close the FD layer. 
+    */
+    int stdout_fileno_copy;
+    stdout_fileno_copy= dup(fileno(stdout)); /* Okay if fileno fails. */
+    if (stdout_fileno_copy == -1)
+      fclose(stdout);
+    else
+      close(stdout_fileno_copy);             /* Clean up dup(). */
+  }
+
   load_defaults("my",load_default_groups,&argc,&argv);
   defaults_argv=argv;
   if (get_options(argc, (char **) argv))

mysql-test/r/mysql_client.result

@@ -2,3 +2,17 @@
 1
 ERROR 1064 (42000) at line 3: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1
 ERROR at line 1: USE must be followed by a database name
+create table t17583 (a int);
+insert into t17583 (a) values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+select count(*) from t17583;
+count(*)
+1280
+drop table t17583;
+End of 4.1 tests.

mysql-test/t/mysql_client.test

@@ -33,3 +33,22 @@
 #
 --exec echo 'help' | $MYSQL   >  $MYSQLTEST_VARDIR/tmp/bug20328.tmp
 --exec echo 'help ' | $MYSQL  >  $MYSQLTEST_VARDIR/tmp/bug20328.tmp
+
+#
+# Bug#17583: mysql drops connection when stdout is not writable
+#
+create table t17583 (a int);
+insert into t17583 (a) values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+insert into t17583 select a from t17583;
+# Close to the minimal data needed to exercise bug.
+select count(*) from t17583;
+--exec echo "select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; select count(*) from t17583; " |$MYSQL test >&-
+drop table t17583;
+
+--echo End of 4.1 tests.