From: Porlock <porlock@mailinator.com>
To: 9fans@9fans.net
Subject: [9fans] snprintf buffer overrun
Date: Sun, 27 Nov 2016 14:58:02 +0000 [thread overview]
Message-ID: <583AF47A.4010400@mailinator.com> (raw)
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Plan 9's implementation of the standard C functions snprintf and
vsnprintf have a buffer overrun bug.
If the buffer length equals the output length (without the terminating
null), then one too many characters is written to the buffer.
For example,
snprintf(buf, 4, "ABCD");
will write 5 characters to buf.
Attached is a short program to illustrate this, which gives the
following output :-
% 8c printftest.c && 8l printftest.8
% ./8.out
A B C D \0 * * * * * * * * * * *
[-- Attachment #2: printftest.c --]
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#include <u.h>
#include <libc.h>
#include <stdio.h>
void main()
{
char buf[16];
int i;
memset(buf, '*', sizeof(buf));
snprintf(buf, 4, "ABCD");
for (i = 0; i < sizeof(buf); ++i) {
if (buf[i])
print(" %c ", buf[i]);
else
print(" \\0");
}
print("\n");
}
next reply other threads:[~2016-11-27 14:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-27 14:58 Porlock [this message]
2016-11-27 20:20 ` cinap_lenrek
2016-11-27 20:31 ` cinap_lenrek
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