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From edc696a73a7cb07b1aa68792a845a98d036ee7eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Bollo?= <jobol@nonadev.net>
Date: Tue, 8 Mar 2022 09:58:16 +0100
Subject: [PATCH] libio: Ensure output buffer for wchars (bug #28828)
The _IO_wfile_overflow does not check if the write pointer for wide
data is valid before access, different than _IO_file_overflow. This
leads to crash on some cases, as described by bug 28828.
The minimal sequence to produce the crash was:
#include <stdio.h>
#include <wchar.h>
int main (int ac, char **av)
{
setvbuf (stdout, NULL, _IOLBF, 0);
fgetwc (stdin);
fputwc (10, stdout); /*CRASH HERE!*/
return 0;
}
The "fgetwc(stdin);" is necessary since it triggers the bug by setting
the flag _IO_CURRENTLY_PUTTING on stdout indirectly (file wfileops.c,
function _IO_wfile_underflow, line 213).
Signed-off-by: Jose Bollo <jobol@nonadev.net>
---
libio/Makefile | 2 +-
libio/tst-bz28828.c | 32 ++++++++++++++++++++++++++++++++
libio/tst-bz28828.input | 1 +
libio/wfileops.c | 3 ++-
4 files changed, 36 insertions(+), 2 deletions(-)
create mode 100644 libio/tst-bz28828.c
create mode 100644 libio/tst-bz28828.input
diff --git a/libio/Makefile b/libio/Makefile
index 0e5f348..e973877 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -66,7 +66,7 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc \
tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof \
tst-sprintf-ub tst-sprintf-chk-ub tst-bz24051 tst-bz24153 \
- tst-wfile-sync
+ tst-wfile-sync tst-bz28828
tests-internal = tst-vtables tst-vtables-interposed
diff --git a/libio/tst-bz28828.c b/libio/tst-bz28828.c
new file mode 100644
index 0000000..638a6e2
--- /dev/null
+++ b/libio/tst-bz28828.c
@@ -0,0 +1,32 @@
+/* Unit test for BZ#28828.
+ Copyright (C) 2022 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 <support/xstdio.h>
+#include <support/check.h>
+#include <wchar.h>
+
+static int
+do_test (void)
+{
+ setvbuf (stdout, NULL, _IOLBF, 0);
+ fgetwc (stdin);
+ fputwc (10, stdout); /* It should not crash here. */
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/libio/tst-bz28828.input b/libio/tst-bz28828.input
new file mode 100644
index 0000000..ce01362
--- /dev/null
+++ b/libio/tst-bz28828.input
@@ -0,0 +1 @@
+hello
diff --git a/libio/wfileops.c b/libio/wfileops.c
index fb9d45b..b59a988 100644
--- a/libio/wfileops.c
+++ b/libio/wfileops.c
@@ -412,7 +412,8 @@ _IO_wfile_overflow (FILE *f, wint_t wch)
return WEOF;
}
/* If currently reading or no buffer allocated. */
- if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0)
+ if ((f->_flags & _IO_CURRENTLY_PUTTING) == 0
+ || f->_wide_data->_IO_write_base == NULL)
{
/* Allocate a buffer if needed. */
if (f->_wide_data->_IO_write_base == 0)
--
1.8.3.1
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