[PATCH] assert.c: Undefine _FORTIFY_SOURCE [BZ 32456]

[H.J. Lu]

When _FORTIFY_SOURCE is defined to >= 1, __printf_buffer, which is
called with (mode_flags & PRINTF_FORTIFY) != 0 via assert (), calls
__readonly_area to check if the format string is readonly.  The
readonly check will fail in 2 cases:
1. When the message is translated and re-encoded, the format string
is writable.
2. When fopen on /proc/self/maps returns NULL due to the malloc
failure, as in test-assert-2.c, __readonly_area return -1.
This triggers the fortification error:

  if (readonly_format < 0)
    __libc_fatal ("*** %n in writable segment detected ***\n");

Undefine _FORTIFY_SOURCE to fix BZ 32456.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
 assert/assert.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/assert/assert.c b/assert/assert.c
index 47b06ec7fd..5446bbde52 100644
--- a/assert/assert.c
+++ b/assert/assert.c
@@ -15,6 +15,21 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+/* When _FORTIFY_SOURCE is defined to >= 1, __printf_buffer, which is
+   called with (mode_flags & PRINTF_FORTIFY) != 0 via assert (), calls
+   __readonly_area to check if the format string is readonly.  The
+   readonly check will fail in 2 cases:
+   1. When the message is translated and re-encoded, the format string
+   is writable.
+   2. When fopen on /proc/self/maps returns NULL due to the malloc
+   failure, as in test-assert-2.c, __readonly_area return -1.
+   This triggers the fortification error:
+
+     if (readonly_format < 0)
+       __libc_fatal ("*** %n in writable segment detected ***\n");
+
+   Undefine _FORTIFY_SOURCE to avoid this error.  */
+#undef _FORTIFY_SOURCE
 #include <assert.h>
 #include <atomic.h>
 #include <ldsodefs.h>
-- 
2.47.1