On Fri, 11 Oct 2002 13:53:01 +0530
"Suresh babu V." <suresh.babu@wipro.com> wrote:
>Hi, While attempting for some testing with sethostname() call, I got
>this problem . As explained in the man page the sethostname call is
>failing(ret val = -1 & errno = EFAULT(14)) for invalid address and
>valid length. But the problem is after running the following test,
>hostname is getting reset to NULL. I tested in both 2.4 & 2.5
>kernels.
[..]
> I saw the code of sys_sethostname() function (sys.c) , in which
>copy_from_user() is being called. I would like to know is it required
>to validate the name argument before calling copy_from_user() to
>avoid such problems.
Please look at copy_from_user() code.
#define copy_from_user(to,from,n) \
(__builtin_constant_p(n) ? \
__constant_copy_from_user((to),(from),(n)) : \
__generic_copy_from_user((to),(from),(n)))
static inline unsigned long
__constant_copy_from_user(void *to, const void *from, unsigned long n)
{
if (access_ok(VERIFY_READ, from, n))
__constant_copy_user_zeroing(to,from,n);
else
memset(to, 0, n);
return n;
}
unsigned long
__generic_copy_from_user(void *to, const void *from, unsigned long n)
{
prefetchw(to);
if (access_ok(VERIFY_READ, from, n))
__copy_user_zeroing(to,from,n);
else
memset(to, 0, n);
return n;
}
So, when in your code example, copy_from_user() fails (returning n)
errno was previously set to -EFAULT in sys_sethostname() as you saw
but memset was invoked so setting hostname to NULL.
Regards,
Angelo Dell'Aera 'buffer'
<buffer@users.sourceforge.net>
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