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userns: Better restrictions on when proc and sysfs can be mounted

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Rely on the fact that another flavor of the filesystem is already
mounted and do not rely on state in the user namespace.

Verify that the mounted filesystem is not covered in any significant
way.  I would love to verify that the previously mounted filesystem
has no mounts on top but there are at least the directories
/proc/sys/fs/binfmt_misc and /sys/fs/cgroup/ that exist explicitly
for other filesystems to mount on top of.

Refactor the test into a function named fs_fully_visible and call that
function from the mount routines of proc and sysfs.  This makes this
test local to the filesystems involved and the results current of when
the mounts take place, removing a weird threading of the user
namespace, the mount namespace and the filesystems themselves.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2013-03-30 19:57:41 -07:00
parent 4ce5d2b1a8
commit e51db73532
7 changed files with 33 additions and 23 deletions
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4
include/linux/user_namespace.h
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@ -26,8 +26,6 @@ struct user_namespace {
kuid_t owner;
kgid_t group;
unsigned int proc_inum;
bool may_mount_sysfs;
bool may_mount_proc;
};
extern struct user_namespace init_user_ns;
@ -84,6 +82,4 @@ static inline void put_user_ns(struct user_namespace *ns)
#endif
void update_mnt_policy(struct user_namespace *userns);
#endif /* _LINUX_USER_H */