[ale] cannot open -> /proc/####/mem huh ?
Courtney Thomas
courtneycthomas at bellsouth.net
Thu Feb 9 09:59:26 EST 2012
Thank you Jim.
I'm incomprehending at to why such was instigated to begin with :-{
Cordially,
Courtney
On 02/08/12 08:43, Jim Kinney wrote:
>
> To sum up, /proc is not a place where humans write. It is literally a
> view into kernel processes.
> There are some runtime variables that can be tweaked by admins. For
> most situations these are best handled by sysctl. Most, if not all of
> these, have been relocated to /sys (or I have this all wrong and
> backwards between sys and proc).
>
> On Feb 7, 2012 6:51 PM, "Michael H. Warfield" <mhw at wittsend.com
> <mailto:mhw at wittsend.com>> wrote:
>
> On Tue, 2012-02-07 at 11:46 -0500, Courtney Thomas wrote:
> > Jim,
> >
> > As always.... thanks for your reply.
> >
> > You were correct that kvm was apparently attempting to write to
> /proc~.
> >
> > The puzzle for me is that... there is no /proc/~/mem to which to
> write,
> > but... apparently this is not permissible by design, as I'm not
> allowed
> > to change /proc's 555 permissions.
> >
> > Can /proc's permissions be changed from 555 to, say, 755, and if
> so how;
> > for when I attempt this I get the error that "this is not
> supported" ? I
> > must say, though, that /proc is the only subdir in it's dir whose
> > permissions are not set 755.
>
> It will not help. /proc/.../mem is special and there was recently a
> security advisory on how it was handled in 2.6.29 and above (2.6.26 if
> you are on RedHat 6.2 / CentOS 6.2 / SL 6.2). Permission to write
> to /proc/.../mem was only recently enabled at all and then
> restricted to
> some very specific circumstances (self and certain tracing / debugging
> functions). Unfortunately, the handling of those circumstances proved
> to be flawed resulting in an escalation of privilege by a local
> user on
> the system, which Linus then quickly fixed.
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e268337dfe26dfc7efd422a804dbb27977a3cccc
> http://www.computerworld.com/s/article/9223675/Linux_vendors_rush_to_patch_privilege_escalation_flaw_after_root_exploits_emerge
> https://rhn.redhat.com/errata/RHSA-2012-0052.html
> https://www.redhat.com/security/data/cve/CVE-2012-0056.html
>
> In kernel space, we do not honor permissions, we enforce them. If the
> code path says "if foo then return error = EPERM" your screwed no
> matter
> what you set the permissions to.
>
> If you want to read a really detailed analysis of what it takes to
> exploit this and just how convoluted these exploits can be you can
> check
> out this blog posting here (includes a link to proof of concept
> exploit
> code)...
>
> http://blog.zx2c4.com/749
>
> > More mystifyingly... there are other entries that ARE written to in
> > /proc's subdirs. Huh ? I assumed, apparently wrongly, that if a
> dir's
> > permissions disallowed writing, then it's subdirs would also not
> allow
> > writing.
> >
> > I am also disallowed from changing proc's 'chown'.
> >
> > Finally, when I - cat /proc/version - I get that Linux is version
> > 2.6.16. Does this tell you anything ?
> >
> > Bedazzled and befuddled, as usual :-)
> >
> > Courtney
> >
> >
> > On 02/06/12 19:27, Jim Kinney wrote:
> > >
> > > The first looks like kvm thinks it should be doing something.
> If you
> > > aren't running a kvm based server, disable kvm.
> > > The sendmail issue os literally the daemon can't write the file.
> > > Either disk full or permission error. For unknown reasons
> sometimes
> > > the var/mail becomes not gtoup writeable. A perm change fixed
> it and
> > > it didn't reappear.
> > >
> > > On Feb 6, 2012 1:13 PM, "Courtney Thomas"
> > > <courtneycthomas at bellsouth.net
> <mailto:courtneycthomas at bellsouth.net>
> <mailto:courtneycthomas at bellsouth.net
> <mailto:courtneycthomas at bellsouth.net>>>
> > > wrote:
> > >
> > > What is the significance of this error which is regularly
> appearing in
> > > /var/log/messages along with.....
> > >
> > > kvm_getenvv
> > >
> > > failed ?
> > >
> > > This is apparently aroused by gnome's "console-kit-daemon"
> > >
> > >
> ______________________________________________________________________________________________
> > >
> > >
> > > I'm also getting what I assume is a sendmail complaint as
> follows:
> > >
> > > sm-mta cannot write .q###############: permission denied.
> > >
> > > How can I resolve this as well, pleasely,
> > >
> > > C.Thomas
> > > _______________________________________________
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> > >
> > >
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> --
> Michael H. Warfield (AI4NB) | (770) 985-6132
> <tel:%28770%29%20985-6132> | mhw at WittsEnd.com
> /\/\|=mhw=|\/\/ | (678) 463-0932
> <tel:%28678%29%20463-0932> | http://www.wittsend.com/mhw/
> NIC whois: MHW9 | An optimist believes we live in the
> best of all
> PGP Key: 0x674627FF | possible worlds. A pessimist is
> sure of it!
>
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