From: Pontus Jensen Karlsson <pontus@jensenkarlsson.se>
To: musl@lists.openwall.com
Subject: [musl] Potential bug in printf_core
Date: Fri, 6 Aug 2021 15:14:22 +0200 [thread overview]
Message-ID: <23e62796-4efb-3495-d7c8-1e3d85f4ea82@jensenkarlsson.se> (raw)
Hi,
I've been trying to build audit-userspace tools for an ARMv7 SBC using
musl 1.2.2 as libc.
The tool auditd continously segfaults and I've traced it to a printf
statement that
I have isolated the issue to this piece of code (simplified for
debugging purposes):
#include <sys/time.h>
#include <stdio.h>
int main(int argc, char **argv)
{
struct timeval tv = {
.tv_sec = 1000,
.tv_usec = 4177777
};
char *str = "Hello World";
unsigned num = 8062;
printf("%lu %03u %u %s", tv.tv_sec, (unsigned)(tv.tv_usec), num, str);
}
This code segfaults at memchr (s = 0x3fbf71 <error: Cannot access memory
at address 0x3fbf71>)
but three frames up we're at src/stdio/vfprintf.c:593.
Here it attempts to read the string length from the arg.p address, the
problem is that arg.p points
to the int-value of (unsigned)(tv.tv_usec) and not the memory address of
str.
So, I'm confused as to why this happens? Is it something weird with the
state-machine in printf_core,
or am I misunderstanding something which needs to be patched into
audit-userspace?
Best regards,
Pontus Jensen Karlsson
next reply other threads:[~2021-08-06 13:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 13:14 Pontus Jensen Karlsson [this message]
2021-08-06 14:20 ` Rich Felker
2021-08-06 19:29 ` Pontus Jensen Karlsson
2021-08-06 19:35 ` Érico Nogueira
2021-08-06 19:36 ` Rich Felker
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