Recent /proc/pid/mem exploit

[David Quigley <selinux@xxxxxxxxxxxxxxx>]

So I read through the recent privilege escalation vulnerability using 
su and gpasswd which exploits weak permission checks in /proc/pid/mem 
and tried to figure out why we didn't stop it. What it comes down to is 
that /proc/pid and everything under it is given the same type as the 
process itself. In the case of the gpasswd that type is groupadd_t. 
Looking at the kernel code for /proc/pid/mem and its read/write 
functions it seems that the only permission checking we do on that node 
is done by the vfs. So from the SELinux perspective you would need allow 
groupadd_t groupadd_t file:{open read write} to have access to 
/proc/pid/mem. For some odd reason tons and tons of applications have 
file:{open read and write} on itself.

One question that should be asked is why is is that we have so many 
rules that contain sometype_t sometype_t file: {open read write}. Is it 
necessary or something that is just being pulled in from a macro. If 
this is necessary for other reasons the followup to this would be should 
/proc/pid/mem have the same type as the process or should we have some 
additional requirements permission wise for a process to read and write 
to its own memory through /proc/pid/mem. What are the valid reasons for 
a process to be poking around through its memory using /proc/pid/mem?

Dave
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