On Tue, Jun 19, 2001 at 07:52:25PM -0700, David S. Miller wrote:
>
> Zack Weinberg writes:
> > It *has* been fixed in 2.4, though. Some sort of compatibility issue?
>
> No, some kind of "it doesn't matter" issue.
I can demonstrate user code that behaves differently under 2.2 than
2.4. The example I have (appended) doesn't suffer data loss, but I
bet I could make one that did.
I don't think it's a security hole, if that's what you mean.
zw
/* Pointer validation hack. Expected output is
* |
* |
* |{null ptr}
* |{unmapped: 0xAFAFAFAF}
* |{unmapped: 0xA5A5A5A5}
* |{unmapped: 0xCDEFABCD}
* |{unaligned: 0xBFFFFB2B}
*
* Under Linux 2.2, will print a blank line instead of each
* {unmapped: 0x...}.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static const char *
validate_ptr(void *p, size_t align)
{
static int pipes[2];
static int setup = 0;
char dummy;
if(!setup)
{
if(pipe(pipes))
abort();
setup = 1;
}
if(p == NULL)
return "{null ptr}";
if((unsigned long)p & (align - 1))
return "{unaligned: 0x%lX}";
if(write(pipes[1], p, 1) != 1)
return "{unmapped: 0x%lX}";
/* clear out the byte we just wrote down the pipe */
read(pipes[0], &dummy, 1);
return 0;
}
int
main(void)
{
char blah = 'x';
char *a, *b, *c, *d, *e, *f;
const char *msg;
a = &blah;
b = malloc(1);
c = (char *) 0;
d = (char *) 0xafafafaf;
e = (char *) 0xa5a5a5a5;
f = (char *) 0xcdefabcd;
#define TEST(x, y) \
if((msg = validate_ptr(x, y))) printf(msg, (unsigned long)x); \
putchar('\n');
TEST(a, 1);
TEST(b, 4);
TEST(c, 1);
TEST(d, 1);
TEST(e, 1);
TEST(f, 1);
TEST(a, 2);
return 0;
}
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