Interaction user namespace, /proc/1 ownership & cap_set

Gao feng gaofeng at
Tue Jul 2 05:14:59 UTC 2013

On 07/02/2013 12:16 AM, Daniel P. Berrange wrote:
> I'm struggling debugging a strange problem with interaction between user
> namespaces, cap_set and ownership of files in /proc/1/

This problem is occured after we call setuid/gid.

for example, a task whose pid is 1234 calls

The uid/gid of the /proc/1234 is 10:0
ll /proc/1234 -d
dr-xr-xr-x 8 uucp wheel 0 Jul  2 10:57 /proc/1234

the uid/gid of the files under /proc/1234 are two kinds...
ll /proc/1234
dr-xr-xr-x 2 uucp wheel 0 Jul  2 10:58 attr
-rw-r--r-- 1 root root 0 Jul  2 10:58 autogroup
dr-xr-xr-x 5 uucp wheel 0 Jul  2 10:58 net
dr-x--x--x 2 root root 0 Jul  2 10:58 ns
dr-xr-xr-x 3 uucp wheel 0 Jul  2 10:58 task

I checked the pre_revalidate and found the owner of the files under /proc/<pid>
will be set to the GLOBAL_ROOT_UID if the task executed setuid/setgid(task_dumpable is false).
Is this what we expected? why?  For user namespace,the owner of /proc/1/* is incorrect and
after task call setuid/gid in user namespace, the owner of /proc/<pid-of-this-task>/* is incorrect

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