Messages in this thread |  | | Date | Sat, 11 Dec 2021 09:29:01 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH v6 15/17] ima: Use mac_admin_ns_capable() to check corresponding capability |
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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@huawei.com> > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> > --- > 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
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