On Fri, Dec 10, 2021 at 02:47:34PM -0500, Stefan Berger wrote:
> Use mac_admin_ns_capable() to check corresponding capability to allow
> read/write IMA policy without CAP_SYS_ADMIN but with CAP_MAC_ADMIN.
>
> Signed-off-by: Denis Semakin <denis.semakin@xxxxxxxxxx>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
> include/linux/capability.h | 6 ++++++
> security/integrity/ima/ima_fs.c | 2 +-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 65efb74c3585..991579178f32 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
> ns_capable(ns, CAP_SYS_ADMIN);
> }
>
> +static inline bool mac_admin_ns_capable(struct user_namespace *ns)
> +{
> + return ns_capable(ns, CAP_MAC_ADMIN) ||
> + ns_capable(ns, CAP_SYS_ADMIN);
> +}
> +
> /* audit system wants to get cap info from files as well */
> int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
> const struct dentry *dentry,
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index a136d14f29ec..090ee85bfa3a 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -440,7 +440,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
> #else
> if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
> return -EACCES;
> - if (!capable(CAP_SYS_ADMIN))
> + if (!mac_admin_ns_capable(user_ns))
Sorry if I'm missing something. But I'm looking at your tree's
version of ima_update_policy() and failing to see where it adds
extra capability checks. Note that any unprivileged user can
unshare a user namespace, map its hostuid to nsuid 0, and pass
ns_capable(CAP_MAC_ADMIN).
Likewise, a host uid 0 process which does not have CAP_MAC_ADMIN
can create a new user namespace, map hostuid 0 to nsuid 0, and
have CAP_MAC_ADMIN against the new userns.
Somewhere you need to be checking for privilege against either
the parent ns or the init_user_ns. I'm not seeing where that's
being done. Can you point me to it?
> return -EPERM;
> return ima_seq_open(filp, &ima_policy_seqops);
> #endif
> --
> 2.31.1
