Fix double free in __printf_fp_l (bug 26214).

__printf_fp_l has a double free bug in the case where it allocates
memory with malloc internally, then has an I/O error while outputting
trailing padding and tries to free that already-freed memory when the
error occurs.  This patch fixes this by setting the relevant pointer
to NULL after the first free (the only free of this pointer that isn't
immediately followed by returning from the function).

Tested for x86_64 and x86.

1 files changed, 37 insertions, 0 deletions

diff --git a/stdio-common/tst-printf-fp-free.c b/stdio-common/tst-printf-fp-free.c
new file mode 100644
index 0000000000..fea52248e0
--- /dev/null
+++ b/stdio-common/tst-printf-fp-free.c
@@ -0,0 +1,37 @@
+/* Test double free bug in __printf_fp_l (bug 26214).
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <mcheck.h>
+#include <stdio.h>
+#include <sys/resource.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  mtrace ();
+  FILE *fp = fopen ("/dev/full", "w");
+  TEST_VERIFY_EXIT (fp != NULL);
+  char buf[131072];
+  TEST_VERIFY_EXIT (setvbuf (fp, buf, _IOFBF, sizeof buf) == 0);
+  TEST_COMPARE (fprintf (fp, "%-1000000.65536f", 1.0), -1);
+  fclose (fp);
+  return 0;
+}
+
+#include <support/test-driver.c>