lkml.org 
[lkml]   [2006]   [Aug]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] set*uid() must not fail-and-return on OOM/rlimits
Alan Cox wrote:
> Ar Llu, 2006-08-21 am 02:12 +0400, ysgrifennodd Solar Designer:
>> Are you referring to killing of processes on OOM? That was in Linux
>> already, this patch does not introduce it.
>
> (pedantic) Only if you have overcommit disabled.
>
>> As it relates to setuid() in particular, POSIX.1-2001 says:
>>
>> The setuid() function shall fail, return -1, and set errno to the
>> corresponding value if one or more of the following are true:
>>
>> [EINVAL]
>> The value of the uid argument is invalid and not supported by
>> the implementation.
>> [EPERM] The process does not have appropriate privileges and uid does
>> not match the real user ID or the saved set-user-ID.
>>
>> No other error conditions are defined.
>
>> I'd say that the behavior of returning EAGAIN is non-compliant.
>
> You are allowed to return other errors. What you must not do is return a
> different error for the description described in the text as I
> understand it.
>
>> But the kills are needed. They are more correct and safer than
>> returning EAGAIN. An alternative would be to not allocate memory on
>> set*uid() at all - like we did not in older kernels - but that would
>> be an inappropriate behavior change for 2.4.
>
> It is certainly an awkward case to get right when setuid code is not
> being audited but I still think you are chasing the symptom, and its not
> symptom of crap code, so you are not likely to "fix" security. A lot of
> BSD code for example doesn't check malloc returns but you don't want an
> auto-kill if mmap fails ?
>
> The kill has the advantage that it stops the situation but it may also
> be that you kill a program which can handle the case and you create a
> new DoS attack (eg against a daemon switching to your uid). The current
> situation is not good, the updated situation could be far worse.
>
> The message is important, we want to know it happened in the memory
> shortage case anyway.

How about going ahead with the uid change (if the current user is root)
BUT still return -EAGAIN. That way programs that ignore the return
value will at least no longer have root privileges.

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-08-21 02:27    [W:0.058 / U:0.248 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site