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SubjectRe: [CHECKER] copy_*_user length bugs?
On Tue, Apr 17, 2001 at 09:39:15PM -0700, Dawson Engler wrote:
> Hi All,
>
> at the suggestion of Chris (chris@ferret.lmh.ox.ac.uk) I wrote a simple
> checker to warn when the length parameter to copy_*_user was (1) an
> integer and (2) not checked < 0.
>
> As an example, the ipv6 routine rawv6_geticmpfilter gets an integer 'len'
> from user space, checks that it is smaller than a struct size and then
> uses length as an argument to copy_to_user:
>
> if (get_user(len, optlen))
> return -EFAULT;
> if (len > sizeof(struct icmp6_filter))
> len = sizeof(struct icmp6_filter);
> if (put_user(len, optlen))
> return -EFAULT;
> if (copy_to_user(optval, &sk->tp_pinfo.tp_raw.filter, len))
> return -EFAULT;
>
> Is this a real bug? Or is the checked rule only applicable to
> __copy_*_user routines rather than copy_*_user routines? (If its a real
> bug, theres about 8 others that we found).


The len parameter is an unsigned value, so this code is ok as
long as access_ok() correctly checks that the range to copy
doesn't stray outside of the userspace range, including the
possible wraparound for a very large len. access_ok() on i386
checks for the wraparound. m68k doesn't use it. PowerPC
is correct, but only because TASK_SIZE is 0x80000000. If it
is ever changed, there could be a problem. I didn't check
other architectures, because I don't understand the asm.



dave...

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