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Message-Id: <20230414145543.2877269-1-gabravier@gmail.com>
Date: Fri, 14 Apr 2023 16:55:42 +0200
From: Gabriel Ravier <gabravier@...il.com>
To: musl@...ts.openwall.com
Cc: Gabriel Ravier <gabravier@...il.com>
Subject: [PATCH] fix wide printf numbered argument buffer overflow
The nl_type and nl_arg arrays defined in vfwprintf may be accessed
with an index up to and including NL_ARGMAX, but they are only of size
NL_ARGMAX, meaning they may be written to or read from 1 element too
far.
For example, the following program:
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <wchar.h>
int main(void) {
char buffer[500];
for (size_t i = 0; i < sizeof(buffer); ++i)
buffer[i] = (i % 3) ? 0 : 42;
wchar_t result;
int ret = swprintf(&result, 1, L"%1$s", "");
assert(ret != -1);
}
evidences the bug, by sometimes mistakenly failing the assertion
and always triggering a warning under valgrind (the behavior is highly
dependent on build configuration - I could only reproduce the assert
failure with GCC 12.2.1 on a very specific system - but the bug is
still there, as evidenced by the warning valgrind always emits)
This patch fixes this.
---
src/stdio/vfwprintf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/stdio/vfwprintf.c b/src/stdio/vfwprintf.c
index 18784113..53697701 100644
--- a/src/stdio/vfwprintf.c
+++ b/src/stdio/vfwprintf.c
@@ -347,8 +347,8 @@ overflow:
int vfwprintf(FILE *restrict f, const wchar_t *restrict fmt, va_list ap)
{
va_list ap2;
- int nl_type[NL_ARGMAX] = {0};
- union arg nl_arg[NL_ARGMAX];
+ int nl_type[NL_ARGMAX+1] = {0};
+ union arg nl_arg[NL_ARGMAX+1];
int olderr;
int ret;
--
2.39.2
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