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Re: ext3 hacked filesystem (by debian exim4 exploit) available for analy


From: Luke Kenneth Casson Leighton
Subject: Re: ext3 hacked filesystem (by debian exim4 exploit) available for analysis and bugreporting
Date: Sat, 30 Jul 2011 14:15:27 +0100

2011/7/29 Pádraig Brady <address@hidden>:
> On 07/29/2011 10:31 PM, Matthias Schniedermeyer wrote:
>> On 29.07.2011 21:59, Pavel Machek wrote:
>>> On Mon 2011-07-25 22:08:24, Luke Kenneth Casson Leighton wrote:
>>>> On Mon, Jul 25, 2011 at 2:45 PM, Matthias Schniedermeyer <address@hidden> 
>>>> wrote:
>>>>> On 25.07.2011 13:08, Luke Kenneth Casson Leighton wrote:
>>>>>> folks, hi,
>>>>>>
>>>>>> apart from anything, files which cannot be deleted (and cannot be
>>>>>> detected as "corrupted" by fsck.ext3) is pretty damn serious.
>>>>>
>>>>> You did try lsattr and checked that the files aren't 'immutable'?
>>>>
>>>>  i didn't! :)  didn't know about (but should have guessed) ext3
>>>> attributes.  they are indeed - thank you matthias.
>>>>
>>>> address@hidden:/mnt/horsebox/tmp3# lsattr *
>>>> ----ia------------- bin3/kill
>>>> ----ia------------- bin3/ps
>>>> ----ia------------- c.pl
>>>> ----ia------------- e.conf
>>>> ----ia------------- sbin3/sysctl
>>>> ----ia------------- usrbin3/uptime
>>>> ----ia------------- usrbin3/tload
>>>> ----ia------------- usrbin3/free
>>>> ----ia------------- usrbin3/top
>>>> ----ia------------- usrbin3/vmstat
>>>> ----ia------------- usrbin3/watch
>>>> ----ia------------- usrbin3/skill
>>>> ----ia------------- usrbin3/pmap
>>>> ----ia------------- usrbin3/pgrep
>>>> ----ia------------- usrbin3/slabtop
>>>> ----ia------------- usrbin3/pwdx
>>>> ----ia------------- usrbin3/snice
>>>> ----ia------------- usrbin3/pkill
>>>> ----ia------------- usrbin3/w
>>>>
>>>> so - looks like it's not as bad as i thought.
>>>
>>> Should ls -l be moddified to show something when file has immutable
>>> (and friends) set?
>>
>> AFAICT lsattr, in e2fsprogs, only does a 'stat'(lib/e2p/fgetflags.c) and
>> checks st_flags, which i can't see in the "man 2 stat"-man-page i have
>> installed, but nonetheless that is what it appears to do.
>>
>> So assuming there are no incompatibilites between filesystems, the
>> information appears to come "free" with the stat(s) that ls has to do
>> anyway. (In the sense that there doesn't appear to any excessive
>> overhead involved, especially no additional I/O).
>>
>> So i would say: definitly.
>
> `strace lsattr ...` shows it calls ioctl (...FS_IOC_GETFLAGS...)
> So there would be overhead.

$ strace -o log.txt ls -altr

 ...
 ...
 lstat(".", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
lgetxattr(".", "security.selinux", 0xeb5bf0, 255) = -1 ENODATA (No
data available)
getxattr(".", "system.posix_acl_access", 0x0, 0) = -1 EOPNOTSUPP
(Operation not supported)
 ...

so it looks like there already is overhead.

on the basis that "ls" is already looking for selinux extended
attributes, as well as.. oh - posix ACLs as well! - i'd say that
adding an extra call to check even the existence of anything that
lsattr does (not _what_ they are, just "are there any at all?") would
not be, relatively speaking, that much extra.

l.



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