Messages in this thread | | | From | Roland McGrath <> | Subject | Re: Q: sys_personality() && misc oddities | Date | Wed, 26 May 2010 13:31:05 -0700 (PDT) |
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> > 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
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