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Date: Wed, 22 Mar 2023 17:24:18 +0100
From: Bruno Haible <bruno@...sp.org>
To: musl@...ts.openwall.com
Subject: swprintf produces garbage after a null wide character
When swprintf is meant to produce output with a null wide character, in
musl libc 1.2.3, it produces a correct return value, but fills the entire
destination buffer with null wide characters. I.e. in this case, the number
of written wide characters is larger than the return value + 1.
How to reproduce:
==================================== foo.c ====================================
#include <stdio.h>
#include <wchar.h>
int main ()
{
{
wchar_t buf[5] = { 0xBEEF, 0xBEEF, 0xBEEF, 0xBEEF, 0xBEEF };
int ret = swprintf (buf, 4, L"%c", '\0');
printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[2] = 0x%x, buf[3] = 0x%x, buf[4] = 0x%x\n",
ret,
(unsigned int) buf[0], (unsigned int) buf[1],
(unsigned int) buf[2], (unsigned int) buf[3],
(unsigned int) buf[4]);
}
{
wchar_t buf[5] = { 0xBEEF, 0xBEEF, 0xBEEF, 0xBEEF, 0xBEEF };
int ret = swprintf (buf, 4, L"%cz", '\0');
printf ("ret = %d, buf[0] = 0x%x, buf[1] = 0x%x, buf[2] = 0x%x, buf[3] = 0x%x, buf[4] = 0x%x\n",
ret,
(unsigned int) buf[0], (unsigned int) buf[1],
(unsigned int) buf[2], (unsigned int) buf[3],
(unsigned int) buf[4]);
}
return 0;
}
/*
glibc, Solaris 11, Cygwin:
ret = 1, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0xbeef, buf[3] = 0xbeef, buf[4] = 0xbeef
ret = 2, buf[0] = 0x0, buf[1] = 0x7a, buf[2] = 0x0, buf[3] = 0xbeef, buf[4] = 0xbeef
musl libc:
ret = 1, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0x0, buf[3] = 0x0, buf[4] = 0xbeef
ret = 2, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0x0, buf[3] = 0x0, buf[4] = 0xbeef
FreeBSD 13, NetBSD 9, OpenBSD 7.2, macOS 12.5, AIX 7.1:
ret = 1, buf[0] = 0x0, buf[1] = 0xbeef, buf[2] = 0xbeef, buf[3] = 0xbeef, buf[4] = 0xbeef
ret = 2, buf[0] = 0x0, buf[1] = 0xbeef, buf[2] = 0xbeef, buf[3] = 0xbeef, buf[4] = 0xbeef
*/
===============================================================================
$ gcc -Wall foo.c
$ ./a.out
Expected output:
ret = 1, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0xbeef, buf[3] = 0xbeef, buf[4] = 0xbeef
ret = 2, buf[0] = 0x0, buf[1] = 0x7a, buf[2] = 0x0, buf[3] = 0xbeef, buf[4] = 0xbeef
Actual output:
ret = 1, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0x0, buf[3] = 0x0, buf[4] = 0xbeef
ret = 2, buf[0] = 0x0, buf[1] = 0x0, buf[2] = 0x0, buf[3] = 0x0, buf[4] = 0xbeef
Bruno
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