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userns: Don't allow unprivileged creation of gid mappings

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As any gid mapping will allow and must allow for backwards
compatibility dropping groups don't allow any gid mappings to be
established without CAP_SETGID in the parent user namespace.

For a small class of applications this change breaks userspace
and removes useful functionality.  This small class of applications
includes tools/testing/selftests/mount/unprivilged-remount-test.c

Most of the removed functionality will be added back with the addition
of a one way knob to disable setgroups.  Once setgroups is disabled
setting the gid_map becomes as safe as setting the uid_map.

For more common applications that set the uid_map and the gid_map
with privilege this change will have no affect.

This is part of a fix for CVE-2014-8989.

Cc: stable@vger.kernel.org
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2014-12-05 18:14:19 -06:00
parent 273d2c67c3
commit be7c6dba23
1 changed files with 0 additions and 4 deletions
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4
kernel/user_namespace.c
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@ -821,10 +821,6 @@ static bool new_idmap_permitted(const struct file *file,
kuid_t uid = make_kuid(ns->parent, id);
if (uid_eq(uid, file->f_cred->fsuid))
return true;
} else if (cap_setid == CAP_SETGID) {
kgid_t gid = make_kgid(ns->parent, id);
if (gid_eq(gid, file->f_cred->fsgid))
return true;
}
}