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SubjectRe: thoughts on kernel security issues
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Valdis.Kletnieks@vt.edu wrote:
> On Wed, 26 Jan 2005 14:31:00 EST, John Richard Moser said:
>
>
>>[*] Grsecurity
>> Security Level (Custom) --->
>> Address Space Protection --->
>> Role Based Access Control Options --->
>> Filesystem Protections --->
>> Kernel Auditing --->
>> Executable Protections --->
>> Network Protections --->
>> Sysctl support --->
>> Logging Options --->
>>
>>?? Address Space Protection ??
>> [ ] Deny writing to /dev/kmem, /dev/mem, and /dev/port
>> [ ] Disable privileged I/O
>> [*] Remove addresses from /proc/<pid>/[maps|stat]
>> [*] Deter exploit bruteforcing
>> [*] Hide kernel symbols
>>
>>Need I continue? There's some 30 or 40 more options I could show. If
>>you can't use your enter, left, right, up, y, n, and ? keys, you're
>>crippled and won't be able to patch and unpatch crap either.
>
>
> Just because I can use my arrow keys doesn't mean I can find which part of
> a 250,000 line patch broke something.
>

I can.

Read Kconfig. Find the CONFIG_* for the option. Find what that
disables in the code. Get to work.

> If it's done as 30 or 40 patches, each of which implements ONE OPTION, then
> it's pretty easy to play binary search to find what broke something.
>

Yes and those patches would implement what's inside #ifdef CONFIG_*'s,
so if turning an option off fixes something, it's fairly equivalent.
I'll let it slide that those patches would likley make "some" changes
that aren't in #ifdef blocks, making it a bit harder to track down,
since those changes can also cause breakage themselves and be even
tougher to track down (though maybe not, just read the patch for
non-blocked-off stuff in some cases).

> And don't give me "it doesn't break anything" - in the past, I've fed at least
> 2 bug fixes on things I found broken back to the grsecurity crew (one was a
> borkage in the process-ID-randomization code, another was a bad parenthesis
> matching breaking the intent of an 'if' in one of the filesystem protection
> checks (symlink or fifo or something like that).

Hmm? I found the PID rand breakage in 2.6.7's gr to be quite annoying
and disabled it. It took me all of 2 minutes to determine that PID
randomization was causing the breakage-- as I enabled it during boot
with an init script, the machine oopsed several times and then panic'd. :)

Heh, divide that 2 minutes by the thousands of people who look at the
code, and you find bugs before they're created :D (j/k)

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