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Fix double free in __printf_fp_l (bug 26214).

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__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.
This commit is contained in:
Joseph Myers 2020-07-09 21:51:49 +00:00
parent c363f834cf
commit ede56038e5
3 changed files with 48 additions and 3 deletions
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11
stdio-common/Makefile
View File

@ -67,7 +67,8 @@ tests := tstscanf test_rdwr test-popen tstgetln test-fseek \
tst-renameat2 tst-bz11319 tst-bz11319-fortify2 \
scanf14a scanf16a \
tst-printf-bz25691 \
tst-vfprintf-width-prec-alloc
tst-vfprintf-width-prec-alloc \
tst-printf-fp-free
test-srcs = tst-unbputc tst-printf tst-printfsz-islongdouble
@ -78,11 +79,13 @@ tests-special += $(objpfx)tst-unbputc.out $(objpfx)tst-printf.out \
$(objpfx)tst-setvbuf1-cmp.out \
$(objpfx)tst-vfprintf-width-prec-mem.out \
$(objpfx)tst-printfsz-islongdouble.out \
$(objpfx)tst-printf-bz25691-mem.out
$(objpfx)tst-printf-bz25691-mem.out \
$(objpfx)tst-printf-fp-free-mem.out
generated += tst-printf-bz18872.c tst-printf-bz18872.mtrace \
tst-printf-bz18872-mem.out \
tst-vfprintf-width-prec.mtrace tst-vfprintf-width-prec-mem.out \
tst-printf-bz25691.mtrace tst-printf-bz25691-mem.out
tst-printf-bz25691.mtrace tst-printf-bz25691-mem.out \
tst-printf-fp-free.mtrace tst-printf-fp-free-mem.out
endif
tests-special += $(objpfx)tst-errno-manual.out
@ -108,6 +111,8 @@ tst-vfprintf-width-prec-ENV = \
MALLOC_TRACE=$(objpfx)tst-vfprintf-width-prec.mtrace
tst-printf-bz25691-ENV = \
MALLOC_TRACE=$(objpfx)tst-printf-bz25691.mtrace
tst-printf-fp-free-ENV = \
MALLOC_TRACE=$(objpfx)tst-printf-fp-free.mtrace
$(objpfx)tst-unbputc.out: tst-unbputc.sh $(objpfx)tst-unbputc
$(SHELL) $< $(common-objpfx) '$(test-program-prefix)' > $@; \

3
stdio-common/printf_fp.c
View File

@ -1250,6 +1250,9 @@ __printf_fp_l (FILE *fp, locale_t loc,
{
free (buffer);
free (wbuffer);
/* Avoid a double free if the subsequent PADN encounters an
I/O error. */
wbuffer = NULL;
}
}

37
stdio-common/tst-printf-fp-free.c Normal file
View File

@ -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>