lkml.org 
[lkml]   [2010]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Q: sys_personality() && misc oddities
Date
> > Though the high bit might be set on 32-bit, there still should not really
> > be a danger of misinterpreting a value as an error code--as long as we
> > haven't used up all 10 of those middle bits. The test userland (glibc)
> > uses is not "long < 0" but "u_long > -4095UL". So as long as at least
> > one bit in 0xff00 remains clear, it won't match.
>
> Yes, libc itself is fine. But from the application's pov, personality()
> returns int, not long.

That doesn't really matter to error/success ambiguity. Since what I said
is true, it won't ever return exactly -1 for a non-error. But even if it
did, the application can use errno=0;personality(x);errno!=0 checking.

> > For 64-bit you want to avoid sign-extension of the old value just so it
> > looks valid (even though it won't look like an error code). I think the
> > most sensible thing is to change the task_struct field to 'unsigned int'.
>
> it is already 'unsigned int' ;)

Ok, then there is no bug right now, is there?

> Yes! and despite the fact it returns -EINVAL, current->personality was
> changed. This can't be right.

Agreed.

> > So, perhaps you are right about checking high
> > bits. Then I'd make it:
> >
> > if ((int) personality != -1) {
> > if (unlikely((unsigned int) personality != personality))
> > return -EINVAL;
>
> Well. Think about personality(0xffffffff - 1). It passes both checks
> and we change current->personality. Then the application calls
> personality() again, we return the old value, and since the user-space
> expects "int" it gets -2.

Yes, it never really made any sense to me that it doesn't validate any of
the flag bits.

> How about
>
> if (personality != 0xffffffff) {
> if (personality >= 0x7fffffff)
> return -EINVAL;
> set_personality(personality);
> }
>
> ? Now that personality always fits into "insigned int" we don't need
> to recheck current->personality == personality, and "< 0x7fffffff"
> gurantees that "int old_personality = personality(whatever)" in user
> space can be never misinterpeted as error.

Sure.

> As for the other oddities, they need the separate patches. Or we can
> just leave this code alone ;)

I can't see any sign that anybody cares.


Thanks,
Roland


\
 
 \ /
  Last update: 2010-05-26 22:33    [W:0.148 / U:0.336 seconds]
©2003-2014 Jasper Spaans. Advertise on this site