Re: [PATCH 11/19] fs: Ensure the mounter of a filesystem is privileged towards its inodes

Serge E. Hallyn
2015-12-04T19:00:20Z

Quoting Seth Forshee (seth.forshee@canonical.com):
> The mounter of a filesystem should be privileged towards the
> inodes of that filesystem. Extend the checks in
> inode_owner_or_capable() and capable_wrt_inode_uidgid() to
> permit access by users priviliged in the user namespace of the
> inode's superblock.
>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
> fs/inode.c | 3 +++
> kernel/capability.c | 13 +++++++++----
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f9003eb3..01c036fe1950 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1962,6 +1962,9 @@ bool inode_owner_or_capable(const struct inode *inode)
> ns = current_user_ns();
> if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
> return true;
> +
> + if (ns_capable(inode->i_sb->s_user_ns, CAP_FOWNER))
> + return true;
> return false;
> }
> EXPORT_SYMBOL(inode_owner_or_capable);
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 45432b54d5c6..5137a38a5670 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -437,13 +437,18 @@ EXPORT_SYMBOL(file_ns_capable);
> *
> * Return true if the current task has the given capability targeted at
> * its own user namespace and that the given inode's uid and gid are
> - * mapped into the current user namespace.
> + * mapped into the current user namespace, or if the current task has
> + * the capability towards the user namespace of the inode's superblock.
> */
> bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
> {
> - struct user_namespace *ns = current_user_ns();
> + struct user_namespace *ns;
>
> - return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
> - kgid_has_mapping(ns, inode->i_gid);
> + ns = current_user_ns();
> + if (ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
> + kgid_has_mapping(ns, inode->i_gid))
> + return true;
> +
> + return ns_capable(inode->i_sb->s_user_ns, cap);
> }
> EXPORT_SYMBOL(capable_wrt_inode_uidgid);
> --
> 1.9.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/