Messages in this thread | | | Date | Fri, 23 Jun 2017 16:09:56 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH 0/3] Enable namespaced file capabilities |
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On Thu, Jun 22, 2017 at 02:59:46PM -0400, Stefan Berger wrote: > This series of patches primary goal is to enable file capabilities > in user namespaces without affecting the file capabilities that are > effective on the host. This is to prevent that any unprivileged user > on the host maps his own uid to root in a private namespace, writes > the xattr, and executes the file with privilege on the host. > > We achieve this goal by writing extended attributes with a different > name when a user namespace is used. If for example the root user > in a user namespace writes the security.capability xattr, the name > of the xattr that is actually written is encoded as > security.capability@uid=1000 for root mapped to uid 1000 on the host. > When listing the xattrs on the host, the existing security.capability > as well as the security.capability@uid=1000 will be shown. Inside the > namespace only 'security.capability', with the value of > security.capability@uid=1000, is visible.
Hi Stefan,
Got a question. If child usernamespace sets a security.capability@uid=1000, can any of the parent namespace remove it?
IOW, I set capability from usernamespace and tried to remove it from host and that failed. Is that expected.
# Inside usernamespce $setcap cat_net_raw+ep foo.txt
# outside user namespace $listxattr foo.txt xattr: security.capability@uid=1000 xattr: security.selinux
# outside user namespace setfattr -x security.capability@uid foo.txt setfattr: foo.txt: Invalid argument
Doing a strace shows removexattr() failed. May this will need fixing?
removexattr("testfile.txt", "security.capability@uid") = -1 EINVAL (Invalid argument)
Vivek
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