On Tue, Apr 9, 2019 at 5:42 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>
> UNIX domain socket connections don't have sufficient
> space in the socket buffer (skb) secmark for more than
> one Linux security module (LSM) to pass data. Expanding
> the secmark has been ruled out as an option. Store the
> necessary data in the socket security blob pointed to
> by the skb socket.
I don't believe this is correct. The secid in the unix_skb_parms is
not the same as the secmark in the sk_buff, and I don't know if we are
necessarily prohibited from expanding it. Also, I don't think you can
just store it in the socket security blob, especially without any form
of locking, as that can be shared across multiple sk_buffs.
>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
> include/linux/security.h | 20 +++++++++++++++++++-
> net/unix/af_unix.c | 14 ++++++++------
> security/security.c | 17 ++++++++++++++++-
> 3 files changed, 43 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index e76d7a9dbe50..c413dcc1905a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -71,6 +71,7 @@ struct ctl_table;
> struct audit_krule;
> struct user_namespace;
> struct timezone;
> +struct sk_buff;
>
> enum lsm_event {
> LSM_POLICY_CHANGE,
> @@ -100,6 +101,22 @@ static inline bool lsm_export_any(struct lsm_export *l)
> ((l->flags & LSM_EXPORT_APPARMOR) && l->apparmor));
> }
>
> +static inline bool lsm_export_equal(struct lsm_export *l, struct lsm_export *m)
> +{
> + if (l->flags != m->flags || l->flags == LSM_EXPORT_NONE)
> + return false;
> + if (l->flags & LSM_EXPORT_SELINUX &&
> + (l->selinux != m->selinux || l->selinux == 0))
> + return false;
> + if (l->flags & LSM_EXPORT_SMACK &&
> + (l->smack != m->smack || l->smack == 0))
> + return false;
> + if (l->flags & LSM_EXPORT_APPARMOR &&
> + (l->apparmor != m->apparmor || l->apparmor == 0))
> + return false;
> + return true;
> +}
> +
> /**
> * lsm_export_secid - pull the useful secid out of a lsm_export
> * @data: the containing data structure
> @@ -143,6 +160,8 @@ static inline void lsm_export_to_all(struct lsm_export *data, u32 secid)
> LSM_EXPORT_APPARMOR;
> }
>
> +extern struct lsm_export *lsm_export_skb(struct sk_buff *skb);
> +
> /* These functions are in security/commoncap.c */
> extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
> int cap, unsigned int opts);
> @@ -174,7 +193,6 @@ extern int cap_task_setnice(struct task_struct *p, int nice);
> extern int cap_vm_enough_memory(struct mm_struct *mm, long pages);
>
> struct msghdr;
> -struct sk_buff;
> struct sock;
> struct sockaddr;
> struct socket;
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 4d4107927ba2..afe9c9f1adeb 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -143,21 +143,23 @@ static struct hlist_head *unix_sockets_unbound(void *addr)
> #ifdef CONFIG_SECURITY_NETWORK
> static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
> {
> - lsm_export_secid(&scm->le, &(UNIXCB(skb).secid));
> + struct lsm_export *ble = lsm_export_skb(skb);
> +
> + *ble = scm->le;
> }
>
> static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
> {
> - lsm_export_to_all(&scm->le, UNIXCB(skb).secid);
> + struct lsm_export *ble = lsm_export_skb(skb);
> +
> + scm->le = *ble;
> }
>
> static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)
> {
> - u32 best_secid;
> -
> - lsm_export_secid(&scm->le, &best_secid);
> - return (best_secid == UNIXCB(skb).secid);
> + return lsm_export_equal(&scm->le, lsm_export_skb(skb));
> }
> +
> #else
> static inline void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
> { }
> diff --git a/security/security.c b/security/security.c
> index 69983ad68233..015c38c882ba 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -46,7 +46,22 @@ static struct kmem_cache *lsm_file_cache;
> static struct kmem_cache *lsm_inode_cache;
>
> char *lsm_names;
> -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init;
> +
> +/* Socket blobs include infrastructure managed data */
> +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = {
> + .lbs_sock = sizeof(struct lsm_export),
> +};
> +
> +/**
> + * lsm_export_skb - pointer to the lsm_export associated with the skb
> + * @skb: the socket buffer
> + *
> + * Returns a pointer to the LSM managed data.
> + */
> +struct lsm_export *lsm_export_skb(struct sk_buff *skb)
> +{
> + return skb->sk->sk_security;
> +}
>
> /* Boot-time LSM user choice */
> static __initdata const char *chosen_lsm_order;
> --
> 2.19.1
>
