<p>To sum up, /proc is not a place where humans write. It is literally a view into kernel processes.<br>
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).</p>
<div class="gmail_quote">On Feb 7, 2012 6:51 PM, "Michael H. Warfield" <<a href="mailto:mhw@wittsend.com">mhw@wittsend.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Tue, 2012-02-07 at 11:46 -0500, Courtney Thomas wrote:<br>
> Jim,<br>
><br>
> As always.... thanks for your reply.<br>
><br>
> You were correct that kvm was apparently attempting to write to /proc~.<br>
><br>
> The puzzle for me is that... there is no /proc/~/mem to which to write,<br>
> but... apparently this is not permissible by design, as I'm not allowed<br>
> to change /proc's 555 permissions.<br>
><br>
> Can /proc's permissions be changed from 555 to, say, 755, and if so how;<br>
> for when I attempt this I get the error that "this is not supported" ? I<br>
> must say, though, that /proc is the only subdir in it's dir whose<br>
> permissions are not set 755.<br>
<br>
It will not help. /proc/.../mem is special and there was recently a<br>
security advisory on how it was handled in 2.6.29 and above (2.6.26 if<br>
you are on RedHat 6.2 / CentOS 6.2 / SL 6.2). Permission to write<br>
to /proc/.../mem was only recently enabled at all and then restricted to<br>
some very specific circumstances (self and certain tracing / debugging<br>
functions). Unfortunately, the handling of those circumstances proved<br>
to be flawed resulting in an escalation of privilege by a local user on<br>
the system, which Linus then quickly fixed.<br>
<br>
<a href="http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e268337dfe26dfc7efd422a804dbb27977a3cccc" target="_blank">http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e268337dfe26dfc7efd422a804dbb27977a3cccc</a><br>
<a href="http://www.computerworld.com/s/article/9223675/Linux_vendors_rush_to_patch_privilege_escalation_flaw_after_root_exploits_emerge" target="_blank">http://www.computerworld.com/s/article/9223675/Linux_vendors_rush_to_patch_privilege_escalation_flaw_after_root_exploits_emerge</a><br>
<a href="https://rhn.redhat.com/errata/RHSA-2012-0052.html" target="_blank">https://rhn.redhat.com/errata/RHSA-2012-0052.html</a><br>
<a href="https://www.redhat.com/security/data/cve/CVE-2012-0056.html" target="_blank">https://www.redhat.com/security/data/cve/CVE-2012-0056.html</a><br>
<br>
In kernel space, we do not honor permissions, we enforce them. If the<br>
code path says "if foo then return error = EPERM" your screwed no matter<br>
what you set the permissions to.<br>
<br>
If you want to read a really detailed analysis of what it takes to<br>
exploit this and just how convoluted these exploits can be you can check<br>
out this blog posting here (includes a link to proof of concept exploit<br>
code)...<br>
<br>
<a href="http://blog.zx2c4.com/749" target="_blank">http://blog.zx2c4.com/749</a><br>
<br>
> More mystifyingly... there are other entries that ARE written to in<br>
> /proc's subdirs. Huh ? I assumed, apparently wrongly, that if a dir's<br>
> permissions disallowed writing, then it's subdirs would also not allow<br>
> writing.<br>
><br>
> I am also disallowed from changing proc's 'chown'.<br>
><br>
> Finally, when I - cat /proc/version - I get that Linux is version<br>
> 2.6.16. Does this tell you anything ?<br>
><br>
> Bedazzled and befuddled, as usual :-)<br>
><br>
> Courtney<br>
><br>
><br>
> On 02/06/12 19:27, Jim Kinney wrote:<br>
> ><br>
> > The first looks like kvm thinks it should be doing something. If you<br>
> > aren't running a kvm based server, disable kvm.<br>
> > The sendmail issue os literally the daemon can't write the file.<br>
> > Either disk full or permission error. For unknown reasons sometimes<br>
> > the var/mail becomes not gtoup writeable. A perm change fixed it and<br>
> > it didn't reappear.<br>
> ><br>
> > On Feb 6, 2012 1:13 PM, "Courtney Thomas"<br>
> > <<a href="mailto:courtneycthomas@bellsouth.net">courtneycthomas@bellsouth.net</a> <mailto:<a href="mailto:courtneycthomas@bellsouth.net">courtneycthomas@bellsouth.net</a>>><br>
> > wrote:<br>
> ><br>
> > What is the significance of this error which is regularly appearing in<br>
> > /var/log/messages along with.....<br>
> ><br>
> > kvm_getenvv<br>
> ><br>
> > failed ?<br>
> ><br>
> > This is apparently aroused by gnome's "console-kit-daemon"<br>
> ><br>
> > ______________________________________________________________________________________________<br>
> ><br>
> ><br>
> > I'm also getting what I assume is a sendmail complaint as follows:<br>
> ><br>
> > sm-mta cannot write .q###############: permission denied.<br>
> ><br>
> > How can I resolve this as well, pleasely,<br>
> ><br>
> > C.Thomas<br>
> > _______________________________________________<br>
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><br>
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Michael H. Warfield (AI4NB) | <a href="tel:%28770%29%20985-6132" value="+17709856132">(770) 985-6132</a> | mhw@WittsEnd.com<br>
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