Does this help – in particular the
read_from_network() function and comments I added?
- Chris
#include
<stdio.h>
#include
<stdlib.h>
typedef unsigned
short uid_t;
static void
dowork(uid_t u);
static int
read_from_network(void);
int main(int
argc, char **argv)
{
int x;
x =
read_from_network();
/* Squish
root (it's not safe to execute dowork() with uid(0) */
if ( x == 0 )
{
printf("Uid %u not allowed.\n", x);
exit(1);
}
dowork(x);
return (0);
} /* main() */
static void
dowork(uid_t u)
{
printf("Doing work as uid %u.\n", u);
} /* dowork() */
static int
read_from_network(void)
{
/* I'm a
sneaky guy and exploited the fact that the return value
* is an int,
although I know only the lower 16 bits will be used.
* This is
how I can end up "doing work" as root. */
return
(0xffff0000);
} /*
read_from_network() */
From:
wireshark-dev-bounces@xxxxxxxxxxxxx
[mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On
Behalf Of Jeff Morriss
Sent: Friday, April 25, 2008 9:34
PM
To: Developer support list for
Wireshark
Subject: Re: [Wireshark-dev]
[Wireshark-commits] rev 25171:/trunk/epan/dissectors/ /trunk/epan/dissectors/:
packet-umts_fp.c
On Fri, Apr 25, 2008 at 7:49 PM, Luis EG Ontanon <luis@xxxxxxxxxxx> wrote:
On Fri, Apr 25, 2008 at 10:17 PM, Jeff Morriss
<jeff.morriss.ws@gmail.com> wrote:
I wouldn't have got this by myself without the explanation but if
you
read the code as:
typedef unsigned short uid_t;
void dowork(uid_t u);
int main() {
int x = read_from_network();
// Squish root (it's not safe to execute dowork() with uid
0)
if ( (x & 0x0000ffff) == 0) exit(1);
// ^^^^^^^^^^^^^
dowork(x);
}
you would have noticed the issue.
I get what he's saying but I just don't get it: why would the compiler
convert from int to unsigned short *before* it has to send the value into the
call to dowork()? E.g., 'x' should be an int until I (explicitly or
implicitly) cast it to something else, non? Actually it should still be
an int after the call to dowork(); it just won't be an int when dowork() gets
it.
Maybe I need to go back to school because I'm feeling very noobish right now.