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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