[ghak90,V9,06/13] audit: add contid support for signalling the audit daemon
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Message ID f01f38dbb3190191e5914874322342700aecb9e1.1593198710.git.rgb@redhat.com
State New
Headers show
Series
  • audit: implement container identifier
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Commit Message

Richard Guy Briggs June 27, 2020, 1:20 p.m. UTC
Add audit container identifier support to the action of signalling the
audit daemon.

Since this would need to add an element to the audit_sig_info struct,
a new record type AUDIT_SIGNAL_INFO2 was created with a new
audit_sig_info2 struct.  Corresponding support is required in the
userspace code to reflect the new record request and reply type.
An older userspace won't break since it won't know to request this
record type.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
 include/linux/audit.h       |  8 ++++
 include/uapi/linux/audit.h  |  1 +
 kernel/audit.c              | 95 ++++++++++++++++++++++++++++++++++++++++++++-
 security/selinux/nlmsgtab.c |  1 +
 4 files changed, 104 insertions(+), 1 deletion(-)

Comments

Paul Moore July 5, 2020, 3:10 p.m. UTC | #1
On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@redhat.com> wrote:
>
> Add audit container identifier support to the action of signalling the
> audit daemon.
>
> Since this would need to add an element to the audit_sig_info struct,
> a new record type AUDIT_SIGNAL_INFO2 was created with a new
> audit_sig_info2 struct.  Corresponding support is required in the
> userspace code to reflect the new record request and reply type.
> An older userspace won't break since it won't know to request this
> record type.
>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  include/linux/audit.h       |  8 ++++
>  include/uapi/linux/audit.h  |  1 +
>  kernel/audit.c              | 95 ++++++++++++++++++++++++++++++++++++++++++++-
>  security/selinux/nlmsgtab.c |  1 +
>  4 files changed, 104 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 5eeba0efffc2..89cf7c66abe6 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -22,6 +22,13 @@ struct audit_sig_info {
>         char            ctx[];
>  };
>
> +struct audit_sig_info2 {
> +       uid_t           uid;
> +       pid_t           pid;
> +       u32             cid_len;
> +       char            data[];
> +};
> +
>  struct audit_buffer;
>  struct audit_context;
>  struct inode;
> @@ -105,6 +112,7 @@ struct audit_contobj {
>         u64                     id;
>         struct task_struct      *owner;
>         refcount_t              refcount;
> +       refcount_t              sigflag;
>         struct rcu_head         rcu;
>  };

It seems like we need some protection in audit_set_contid() so that we
don't allow reuse of an audit container ID when "refcount == 0 &&
sigflag != 0", yes?

> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index fd98460c983f..a56ad77069b9 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -72,6 +72,7 @@
>  #define AUDIT_SET_FEATURE      1018    /* Turn an audit feature on or off */
>  #define AUDIT_GET_FEATURE      1019    /* Get which features are enabled */
>  #define AUDIT_CONTAINER_OP     1020    /* Define the container id and info */
> +#define AUDIT_SIGNAL_INFO2     1021    /* Get info auditd signal sender */
>
>  #define AUDIT_FIRST_USER_MSG   1100    /* Userspace messages mostly uninteresting to kernel */
>  #define AUDIT_USER_AVC         1107    /* We filter this differently */
> diff --git a/kernel/audit.c b/kernel/audit.c
> index a09f8f661234..54dd2cb69402 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -126,6 +126,8 @@ struct auditd_connection {
>  kuid_t         audit_sig_uid = INVALID_UID;
>  pid_t          audit_sig_pid = -1;
>  u32            audit_sig_sid = 0;
> +static struct audit_contobj *audit_sig_cid;
> +static struct task_struct *audit_sig_atsk;

This looks like a typo, or did you mean "atsk" for some reason?

>  /* Records can be lost in several ways:
>     0) [suppressed in audit_alloc]
> @@ -239,7 +241,33 @@ void _audit_contobj_put(struct audit_contobj *cont)
>  {
>         if (!cont)
>                 return;
> -       if (refcount_dec_and_test(&cont->refcount)) {
> +       if (refcount_dec_and_test(&cont->refcount) && !refcount_read(&cont->sigflag)) {
> +               put_task_struct(cont->owner);
> +               list_del_rcu(&cont->list);
> +               kfree_rcu(cont, rcu);
> +       }
> +}

It seems like it might be a good idea to modify the corresponding
_get() to WARN on the reuse of audit container objects where refcount
is zero, similar to the comment I made above.  What do you think?

> +/* rcu_read_lock must be held by caller unless new */
> +static struct audit_contobj *_audit_contobj_get_sig(struct task_struct *tsk)
> +{
> +       struct audit_contobj *cont;
> +
> +       if (!tsk->audit)
> +               return NULL;
> +       cont = tsk->audit->cont;
> +       if (cont)
> +               refcount_set(&cont->sigflag, 1);
> +       return cont;
> +}

If you are going to use a refcount and call this a "get" function you
might as well make it do an increment and not just a set(1).  It a bit
silly with just one auditd per system, but I suppose it will make more
sense when we have multiple audit daemons.  In a related comment, you
probably want to rename "sigflag" to "sigcount" or similar.

In summary, it's either a reference that supports multiple gets/puts
or it's a flag with just an on/off; it shouldn't attempt to straddle
both, that's both confusing and fragile.

> +/* rcu_read_lock must be held by caller */
> +static void _audit_contobj_put_sig(struct audit_contobj *cont)
> +{
> +       if (!cont)
> +               return;
> +       refcount_set(&cont->sigflag, 0);
> +       if (!refcount_read(&cont->refcount)) {
>                 put_task_struct(cont->owner);
>                 list_del_rcu(&cont->list);
>                 kfree_rcu(cont, rcu);
> @@ -309,6 +337,13 @@ void audit_free(struct task_struct *tsk)
>         info = tsk->audit;
>         tsk->audit = NULL;
>         kmem_cache_free(audit_task_cache, info);
> +       rcu_read_lock();
> +       if (audit_sig_atsk == tsk) {
> +               _audit_contobj_put_sig(audit_sig_cid);
> +               audit_sig_cid = NULL;
> +               audit_sig_atsk = NULL;
> +       }
> +       rcu_read_unlock();
>  }
>
>  /**
> @@ -1132,6 +1167,7 @@ static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
>         case AUDIT_ADD_RULE:
>         case AUDIT_DEL_RULE:
>         case AUDIT_SIGNAL_INFO:
> +       case AUDIT_SIGNAL_INFO2:
>         case AUDIT_TTY_GET:
>         case AUDIT_TTY_SET:
>         case AUDIT_TRIM:
> @@ -1294,6 +1330,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
>         struct audit_buffer     *ab;
>         u16                     msg_type = nlh->nlmsg_type;
>         struct audit_sig_info   *sig_data;
> +       struct audit_sig_info2  *sig_data2;
>         char                    *ctx = NULL;
>         u32                     len;
>
> @@ -1559,6 +1596,52 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
>                                  sig_data, sizeof(*sig_data) + len);
>                 kfree(sig_data);
>                 break;
> +       case AUDIT_SIGNAL_INFO2: {
> +               unsigned int contidstrlen = 0;
> +
> +               len = 0;
> +               if (audit_sig_sid) {
> +                       err = security_secid_to_secctx(audit_sig_sid, &ctx,
> +                                                      &len);
> +                       if (err)
> +                               return err;
> +               }
> +               if (audit_sig_cid) {
> +                       contidstr = kmalloc(21, GFP_KERNEL);
> +                       if (!contidstr) {
> +                               if (audit_sig_sid)
> +                                       security_release_secctx(ctx, len);
> +                               return -ENOMEM;
> +                       }
> +                       contidstrlen = scnprintf(contidstr, 20, "%llu", audit_sig_cid->id);
> +               }
> +               sig_data2 = kmalloc(sizeof(*sig_data2) + contidstrlen + len, GFP_KERNEL);
> +               if (!sig_data2) {
> +                       if (audit_sig_sid)
> +                               security_release_secctx(ctx, len);
> +                       kfree(contidstr);
> +                       return -ENOMEM;
> +               }
> +               sig_data2->uid = from_kuid(&init_user_ns, audit_sig_uid);
> +               sig_data2->pid = audit_sig_pid;
> +               if (audit_sig_cid) {
> +                       memcpy(sig_data2->data, contidstr, contidstrlen);
> +                       sig_data2->cid_len = contidstrlen;
> +                       kfree(contidstr);
> +               }
> +               if (audit_sig_sid) {
> +                       memcpy(sig_data2->data + contidstrlen, ctx, len);
> +                       security_release_secctx(ctx, len);
> +               }
> +               rcu_read_lock();
> +               _audit_contobj_put_sig(audit_sig_cid);
> +               rcu_read_unlock();

We probably want to drop the reference in the legacy/AUDIT_SIGNAL_INFO
case too, right?

> +               audit_sig_cid = NULL;
> +               audit_send_reply(skb, seq, AUDIT_SIGNAL_INFO2, 0, 0,
> +                                sig_data2, sizeof(*sig_data2) + contidstrlen + len);
> +               kfree(sig_data2);
> +               break;
> +       }
>         case AUDIT_TTY_GET: {
>                 struct audit_tty_status s;
>                 unsigned int t;
> @@ -2470,6 +2553,11 @@ int audit_signal_info(int sig, struct task_struct *t)
>                 else
>                         audit_sig_uid = uid;
>                 security_task_getsecid(current, &audit_sig_sid);
> +               rcu_read_lock();
> +               _audit_contobj_put_sig(audit_sig_cid);
> +               audit_sig_cid = _audit_contobj_get_sig(current);
> +               rcu_read_unlock();
> +               audit_sig_atsk = t;
>         }
>
>         return audit_signal_info_syscall(t);
> @@ -2532,6 +2620,11 @@ int audit_set_contid(struct task_struct *task, u64 contid)
>                         if (cont->id == contid) {
>                                 /* task injection to existing container */
>                                 if (current == cont->owner) {
> +                                       if (!refcount_read(&cont->refcount)) {
> +                                               rc = -ESHUTDOWN;

Reuse -ENOTUNIQ; I'm not overly excited about providing a lot of
detail here as these are global system objects.  If you must have a
different errno (and I would prefer you didn't), use something like
-EBUSY.


> +                                               spin_unlock(&audit_contobj_list_lock);
> +                                               goto conterror;
> +                                       }
>                                         _audit_contobj_hold(cont);
>                                         newcont = cont;
>                                 } else {
> diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
> index b69231918686..8303bb7a63d0 100644
> --- a/security/selinux/nlmsgtab.c
> +++ b/security/selinux/nlmsgtab.c
> @@ -137,6 +137,7 @@ struct nlmsg_perm {
>         { AUDIT_DEL_RULE,       NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
>         { AUDIT_USER,           NETLINK_AUDIT_SOCKET__NLMSG_RELAY    },
>         { AUDIT_SIGNAL_INFO,    NETLINK_AUDIT_SOCKET__NLMSG_READ     },
> +       { AUDIT_SIGNAL_INFO2,   NETLINK_AUDIT_SOCKET__NLMSG_READ     },
>         { AUDIT_TRIM,           NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
>         { AUDIT_MAKE_EQUIV,     NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
>         { AUDIT_TTY_GET,        NETLINK_AUDIT_SOCKET__NLMSG_READ     },

--
paul moore
www.paul-moore.com
Richard Guy Briggs July 29, 2020, 7 p.m. UTC | #2
On 2020-07-05 11:10, Paul Moore wrote:
> On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> >
> > Add audit container identifier support to the action of signalling the
> > audit daemon.
> >
> > Since this would need to add an element to the audit_sig_info struct,
> > a new record type AUDIT_SIGNAL_INFO2 was created with a new
> > audit_sig_info2 struct.  Corresponding support is required in the
> > userspace code to reflect the new record request and reply type.
> > An older userspace won't break since it won't know to request this
> > record type.
> >
> > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > ---
> >  include/linux/audit.h       |  8 ++++
> >  include/uapi/linux/audit.h  |  1 +
> >  kernel/audit.c              | 95 ++++++++++++++++++++++++++++++++++++++++++++-
> >  security/selinux/nlmsgtab.c |  1 +
> >  4 files changed, 104 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index 5eeba0efffc2..89cf7c66abe6 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -22,6 +22,13 @@ struct audit_sig_info {
> >         char            ctx[];
> >  };
> >
> > +struct audit_sig_info2 {
> > +       uid_t           uid;
> > +       pid_t           pid;
> > +       u32             cid_len;
> > +       char            data[];
> > +};
> > +
> >  struct audit_buffer;
> >  struct audit_context;
> >  struct inode;
> > @@ -105,6 +112,7 @@ struct audit_contobj {
> >         u64                     id;
> >         struct task_struct      *owner;
> >         refcount_t              refcount;
> > +       refcount_t              sigflag;
> >         struct rcu_head         rcu;
> >  };
> 
> It seems like we need some protection in audit_set_contid() so that we
> don't allow reuse of an audit container ID when "refcount == 0 &&
> sigflag != 0", yes?

We have it, see -ESHUTDOWN below.

> > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > index fd98460c983f..a56ad77069b9 100644
> > --- a/include/uapi/linux/audit.h
> > +++ b/include/uapi/linux/audit.h
> > @@ -72,6 +72,7 @@
> >  #define AUDIT_SET_FEATURE      1018    /* Turn an audit feature on or off */
> >  #define AUDIT_GET_FEATURE      1019    /* Get which features are enabled */
> >  #define AUDIT_CONTAINER_OP     1020    /* Define the container id and info */
> > +#define AUDIT_SIGNAL_INFO2     1021    /* Get info auditd signal sender */
> >
> >  #define AUDIT_FIRST_USER_MSG   1100    /* Userspace messages mostly uninteresting to kernel */
> >  #define AUDIT_USER_AVC         1107    /* We filter this differently */
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index a09f8f661234..54dd2cb69402 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -126,6 +126,8 @@ struct auditd_connection {
> >  kuid_t         audit_sig_uid = INVALID_UID;
> >  pid_t          audit_sig_pid = -1;
> >  u32            audit_sig_sid = 0;
> > +static struct audit_contobj *audit_sig_cid;
> > +static struct task_struct *audit_sig_atsk;
> 
> This looks like a typo, or did you mean "atsk" for some reason?

No, I meant atsk to refer specifically to the audit daemon task and not
any other random one that is doing the signalling.  I can change it is
there is a strong objection.

> >  /* Records can be lost in several ways:
> >     0) [suppressed in audit_alloc]
> > @@ -239,7 +241,33 @@ void _audit_contobj_put(struct audit_contobj *cont)
> >  {
> >         if (!cont)
> >                 return;
> > -       if (refcount_dec_and_test(&cont->refcount)) {
> > +       if (refcount_dec_and_test(&cont->refcount) && !refcount_read(&cont->sigflag)) {
> > +               put_task_struct(cont->owner);
> > +               list_del_rcu(&cont->list);
> > +               kfree_rcu(cont, rcu);
> > +       }
> > +}
> 
> It seems like it might be a good idea to modify the corresponding
> _get() to WARN on the reuse of audit container objects where refcount
> is zero, similar to the comment I made above.  What do you think?

This will never happen.  See -ESHUTDOWN below.

> > +/* rcu_read_lock must be held by caller unless new */
> > +static struct audit_contobj *_audit_contobj_get_sig(struct task_struct *tsk)
> > +{
> > +       struct audit_contobj *cont;
> > +
> > +       if (!tsk->audit)
> > +               return NULL;
> > +       cont = tsk->audit->cont;
> > +       if (cont)
> > +               refcount_set(&cont->sigflag, 1);
> > +       return cont;
> > +}
> 
> If you are going to use a refcount and call this a "get" function you
> might as well make it do an increment and not just a set(1).  It a bit
> silly with just one auditd per system, but I suppose it will make more
> sense when we have multiple audit daemons.  In a related comment, you
> probably want to rename "sigflag" to "sigcount" or similar.

I preferred that previously.  I'll go back to that.

> In summary, it's either a reference that supports multiple gets/puts
> or it's a flag with just an on/off; it shouldn't attempt to straddle
> both, that's both confusing and fragile.

Agreed.  I'll switch it back to refcount.

> > +/* rcu_read_lock must be held by caller */
> > +static void _audit_contobj_put_sig(struct audit_contobj *cont)
> > +{
> > +       if (!cont)
> > +               return;
> > +       refcount_set(&cont->sigflag, 0);
> > +       if (!refcount_read(&cont->refcount)) {
> >                 put_task_struct(cont->owner);
> >                 list_del_rcu(&cont->list);
> >                 kfree_rcu(cont, rcu);
> > @@ -309,6 +337,13 @@ void audit_free(struct task_struct *tsk)
> >         info = tsk->audit;
> >         tsk->audit = NULL;
> >         kmem_cache_free(audit_task_cache, info);
> > +       rcu_read_lock();
> > +       if (audit_sig_atsk == tsk) {
> > +               _audit_contobj_put_sig(audit_sig_cid);
> > +               audit_sig_cid = NULL;
> > +               audit_sig_atsk = NULL;
> > +       }
> > +       rcu_read_unlock();
> >  }
> >
> >  /**
> > @@ -1132,6 +1167,7 @@ static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
> >         case AUDIT_ADD_RULE:
> >         case AUDIT_DEL_RULE:
> >         case AUDIT_SIGNAL_INFO:
> > +       case AUDIT_SIGNAL_INFO2:
> >         case AUDIT_TTY_GET:
> >         case AUDIT_TTY_SET:
> >         case AUDIT_TRIM:
> > @@ -1294,6 +1330,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> >         struct audit_buffer     *ab;
> >         u16                     msg_type = nlh->nlmsg_type;
> >         struct audit_sig_info   *sig_data;
> > +       struct audit_sig_info2  *sig_data2;
> >         char                    *ctx = NULL;
> >         u32                     len;
> >
> > @@ -1559,6 +1596,52 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> >                                  sig_data, sizeof(*sig_data) + len);
> >                 kfree(sig_data);
> >                 break;
> > +       case AUDIT_SIGNAL_INFO2: {
> > +               unsigned int contidstrlen = 0;
> > +
> > +               len = 0;
> > +               if (audit_sig_sid) {
> > +                       err = security_secid_to_secctx(audit_sig_sid, &ctx,
> > +                                                      &len);
> > +                       if (err)
> > +                               return err;
> > +               }
> > +               if (audit_sig_cid) {
> > +                       contidstr = kmalloc(21, GFP_KERNEL);
> > +                       if (!contidstr) {
> > +                               if (audit_sig_sid)
> > +                                       security_release_secctx(ctx, len);
> > +                               return -ENOMEM;
> > +                       }
> > +                       contidstrlen = scnprintf(contidstr, 20, "%llu", audit_sig_cid->id);
> > +               }
> > +               sig_data2 = kmalloc(sizeof(*sig_data2) + contidstrlen + len, GFP_KERNEL);
> > +               if (!sig_data2) {
> > +                       if (audit_sig_sid)
> > +                               security_release_secctx(ctx, len);
> > +                       kfree(contidstr);
> > +                       return -ENOMEM;
> > +               }
> > +               sig_data2->uid = from_kuid(&init_user_ns, audit_sig_uid);
> > +               sig_data2->pid = audit_sig_pid;
> > +               if (audit_sig_cid) {
> > +                       memcpy(sig_data2->data, contidstr, contidstrlen);
> > +                       sig_data2->cid_len = contidstrlen;
> > +                       kfree(contidstr);
> > +               }
> > +               if (audit_sig_sid) {
> > +                       memcpy(sig_data2->data + contidstrlen, ctx, len);
> > +                       security_release_secctx(ctx, len);
> > +               }
> > +               rcu_read_lock();
> > +               _audit_contobj_put_sig(audit_sig_cid);
> > +               rcu_read_unlock();
> 
> We probably want to drop the reference in the legacy/AUDIT_SIGNAL_INFO
> case too, right?

Yes, thank you for catching that.  This would be the case of an old
userspace and we don't want that kernel mem/contid leak.

> > +               audit_sig_cid = NULL;
> > +               audit_send_reply(skb, seq, AUDIT_SIGNAL_INFO2, 0, 0,
> > +                                sig_data2, sizeof(*sig_data2) + contidstrlen + len);
> > +               kfree(sig_data2);
> > +               break;
> > +       }
> >         case AUDIT_TTY_GET: {
> >                 struct audit_tty_status s;
> >                 unsigned int t;
> > @@ -2470,6 +2553,11 @@ int audit_signal_info(int sig, struct task_struct *t)
> >                 else
> >                         audit_sig_uid = uid;
> >                 security_task_getsecid(current, &audit_sig_sid);
> > +               rcu_read_lock();
> > +               _audit_contobj_put_sig(audit_sig_cid);
> > +               audit_sig_cid = _audit_contobj_get_sig(current);
> > +               rcu_read_unlock();
> > +               audit_sig_atsk = t;
> >         }
> >
> >         return audit_signal_info_syscall(t);
> > @@ -2532,6 +2620,11 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> >                         if (cont->id == contid) {
> >                                 /* task injection to existing container */
> >                                 if (current == cont->owner) {
> > +                                       if (!refcount_read(&cont->refcount)) {
> > +                                               rc = -ESHUTDOWN;
> 
> Reuse -ENOTUNIQ; I'm not overly excited about providing a lot of
> detail here as these are global system objects.  If you must have a
> different errno (and I would prefer you didn't), use something like
> -EBUSY.

I don't understand the issue of "global system objects" since the only
time this error would be issued is if its own contid were being reused
but it hadn't cleaned up its own references yet by either issuing an
AUDIT_SIGNAL_INFO* request or the targetted audit daemon hadn't cleaned
up yet.  EBUSY could be confused with already having spawned threads or
children, and ENOTUNIQ could indicate that another orchestrator/engine
had stolen its desired contid after we released it and wanted to reuse
it.  This gets me thinking about making reservations for preferred
contids that are otherwise unavailable and making callbacks to indicate
when they become available, but that seems undesirably complex right
now.

> > +                                               spin_unlock(&audit_contobj_list_lock);
> > +                                               goto conterror;
> > +                                       }
> >                                         _audit_contobj_hold(cont);
> >                                         newcont = cont;
> >                                 } else {
> > diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
> > index b69231918686..8303bb7a63d0 100644
> > --- a/security/selinux/nlmsgtab.c
> > +++ b/security/selinux/nlmsgtab.c
> > @@ -137,6 +137,7 @@ struct nlmsg_perm {
> >         { AUDIT_DEL_RULE,       NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
> >         { AUDIT_USER,           NETLINK_AUDIT_SOCKET__NLMSG_RELAY    },
> >         { AUDIT_SIGNAL_INFO,    NETLINK_AUDIT_SOCKET__NLMSG_READ     },
> > +       { AUDIT_SIGNAL_INFO2,   NETLINK_AUDIT_SOCKET__NLMSG_READ     },
> >         { AUDIT_TRIM,           NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
> >         { AUDIT_MAKE_EQUIV,     NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
> >         { AUDIT_TTY_GET,        NETLINK_AUDIT_SOCKET__NLMSG_READ     },
> 
> paul moore

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635
Paul Moore Aug. 21, 2020, 6:48 p.m. UTC | #3
On Wed, Jul 29, 2020 at 3:00 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2020-07-05 11:10, Paul Moore wrote:
> > On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> > >
> > > Add audit container identifier support to the action of signalling the
> > > audit daemon.
> > >
> > > Since this would need to add an element to the audit_sig_info struct,
> > > a new record type AUDIT_SIGNAL_INFO2 was created with a new
> > > audit_sig_info2 struct.  Corresponding support is required in the
> > > userspace code to reflect the new record request and reply type.
> > > An older userspace won't break since it won't know to request this
> > > record type.
> > >
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > ---
> > >  include/linux/audit.h       |  8 ++++
> > >  include/uapi/linux/audit.h  |  1 +
> > >  kernel/audit.c              | 95 ++++++++++++++++++++++++++++++++++++++++++++-
> > >  security/selinux/nlmsgtab.c |  1 +
> > >  4 files changed, 104 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > > index 5eeba0efffc2..89cf7c66abe6 100644
> > > --- a/include/linux/audit.h
> > > +++ b/include/linux/audit.h
> > > @@ -22,6 +22,13 @@ struct audit_sig_info {
> > >         char            ctx[];
> > >  };
> > >
> > > +struct audit_sig_info2 {
> > > +       uid_t           uid;
> > > +       pid_t           pid;
> > > +       u32             cid_len;
> > > +       char            data[];
> > > +};
> > > +
> > >  struct audit_buffer;
> > >  struct audit_context;
> > >  struct inode;
> > > @@ -105,6 +112,7 @@ struct audit_contobj {
> > >         u64                     id;
> > >         struct task_struct      *owner;
> > >         refcount_t              refcount;
> > > +       refcount_t              sigflag;
> > >         struct rcu_head         rcu;
> > >  };
> >
> > It seems like we need some protection in audit_set_contid() so that we
> > don't allow reuse of an audit container ID when "refcount == 0 &&
> > sigflag != 0", yes?
>
> We have it, see -ESHUTDOWN below.

That check in audit_set_contid() is checking ->refcount and not
->sigflag; ->sigflag is more important in this context, yes?

> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index fd98460c983f..a56ad77069b9 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -72,6 +72,7 @@
> > >  #define AUDIT_SET_FEATURE      1018    /* Turn an audit feature on or off */
> > >  #define AUDIT_GET_FEATURE      1019    /* Get which features are enabled */
> > >  #define AUDIT_CONTAINER_OP     1020    /* Define the container id and info */
> > > +#define AUDIT_SIGNAL_INFO2     1021    /* Get info auditd signal sender */
> > >
> > >  #define AUDIT_FIRST_USER_MSG   1100    /* Userspace messages mostly uninteresting to kernel */
> > >  #define AUDIT_USER_AVC         1107    /* We filter this differently */
> > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > index a09f8f661234..54dd2cb69402 100644
> > > --- a/kernel/audit.c
> > > +++ b/kernel/audit.c
> > > @@ -126,6 +126,8 @@ struct auditd_connection {
> > >  kuid_t         audit_sig_uid = INVALID_UID;
> > >  pid_t          audit_sig_pid = -1;
> > >  u32            audit_sig_sid = 0;
> > > +static struct audit_contobj *audit_sig_cid;
> > > +static struct task_struct *audit_sig_atsk;
> >
> > This looks like a typo, or did you mean "atsk" for some reason?
>
> No, I meant atsk to refer specifically to the audit daemon task and not
> any other random one that is doing the signalling.  I can change it is
> there is a strong objection.

Esh, yeah, "atsk" looks too much like a typo ;)  At the very leask add
a 'd' in there, e.g. "adtsk", but something better than that would be
welcome.

> > > @@ -2532,6 +2620,11 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> > >                         if (cont->id == contid) {
> > >                                 /* task injection to existing container */
> > >                                 if (current == cont->owner) {
> > > +                                       if (!refcount_read(&cont->refcount)) {
> > > +                                               rc = -ESHUTDOWN;
> >
> > Reuse -ENOTUNIQ; I'm not overly excited about providing a lot of
> > detail here as these are global system objects.  If you must have a
> > different errno (and I would prefer you didn't), use something like
> > -EBUSY.
>
> I don't understand the issue of "global system objects" since the only
> time this error would be issued is if its own contid were being reused
> but it hadn't cleaned up its own references yet by either issuing an
> AUDIT_SIGNAL_INFO* request or the targetted audit daemon hadn't cleaned
> up yet.  EBUSY could be confused with already having spawned threads or
> children, and ENOTUNIQ could indicate that another orchestrator/engine
> had stolen its desired contid after we released it and wanted to reuse
> it.

All the more reason for ENOTUNIQ.  The point is that the audit
container ID is not available for use, and since the IDs are shared
across the entire system I think we are better off having some
ambiquity here with errnos.

> This gets me thinking about making reservations for preferred
> contids that are otherwise unavailable and making callbacks to indicate
> when they become available, but that seems undesirably complex right
> now.

That is definitely beyond the scope of this work, or rather *should*
be beyond the scope of this work.

Patch
diff mbox series

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 5eeba0efffc2..89cf7c66abe6 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -22,6 +22,13 @@  struct audit_sig_info {
 	char		ctx[];
 };
 
+struct audit_sig_info2 {
+	uid_t		uid;
+	pid_t		pid;
+	u32		cid_len;
+	char		data[];
+};
+
 struct audit_buffer;
 struct audit_context;
 struct inode;
@@ -105,6 +112,7 @@  struct audit_contobj {
 	u64			id;
 	struct task_struct	*owner;
 	refcount_t		refcount;
+	refcount_t		sigflag;
 	struct rcu_head         rcu;
 };
 
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index fd98460c983f..a56ad77069b9 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -72,6 +72,7 @@ 
 #define AUDIT_SET_FEATURE	1018	/* Turn an audit feature on or off */
 #define AUDIT_GET_FEATURE	1019	/* Get which features are enabled */
 #define AUDIT_CONTAINER_OP	1020	/* Define the container id and info */
+#define AUDIT_SIGNAL_INFO2	1021	/* Get info auditd signal sender */
 
 #define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
 #define AUDIT_USER_AVC		1107	/* We filter this differently */
diff --git a/kernel/audit.c b/kernel/audit.c
index a09f8f661234..54dd2cb69402 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -126,6 +126,8 @@  struct auditd_connection {
 kuid_t		audit_sig_uid = INVALID_UID;
 pid_t		audit_sig_pid = -1;
 u32		audit_sig_sid = 0;
+static struct audit_contobj *audit_sig_cid;
+static struct task_struct *audit_sig_atsk;
 
 /* Records can be lost in several ways:
    0) [suppressed in audit_alloc]
@@ -239,7 +241,33 @@  void _audit_contobj_put(struct audit_contobj *cont)
 {
 	if (!cont)
 		return;
-	if (refcount_dec_and_test(&cont->refcount)) {
+	if (refcount_dec_and_test(&cont->refcount) && !refcount_read(&cont->sigflag)) {
+		put_task_struct(cont->owner);
+		list_del_rcu(&cont->list);
+		kfree_rcu(cont, rcu);
+	}
+}
+
+/* rcu_read_lock must be held by caller unless new */
+static struct audit_contobj *_audit_contobj_get_sig(struct task_struct *tsk)
+{
+	struct audit_contobj *cont;
+
+	if (!tsk->audit)
+		return NULL;
+	cont = tsk->audit->cont;
+	if (cont)
+		refcount_set(&cont->sigflag, 1);
+	return cont;
+}
+
+/* rcu_read_lock must be held by caller */
+static void _audit_contobj_put_sig(struct audit_contobj *cont)
+{
+	if (!cont)
+		return;
+	refcount_set(&cont->sigflag, 0);
+	if (!refcount_read(&cont->refcount)) {
 		put_task_struct(cont->owner);
 		list_del_rcu(&cont->list);
 		kfree_rcu(cont, rcu);
@@ -309,6 +337,13 @@  void audit_free(struct task_struct *tsk)
 	info = tsk->audit;
 	tsk->audit = NULL;
 	kmem_cache_free(audit_task_cache, info);
+	rcu_read_lock();
+	if (audit_sig_atsk == tsk) {
+		_audit_contobj_put_sig(audit_sig_cid);
+		audit_sig_cid = NULL;
+		audit_sig_atsk = NULL;
+	}
+	rcu_read_unlock();
 }
 
 /**
@@ -1132,6 +1167,7 @@  static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
 	case AUDIT_ADD_RULE:
 	case AUDIT_DEL_RULE:
 	case AUDIT_SIGNAL_INFO:
+	case AUDIT_SIGNAL_INFO2:
 	case AUDIT_TTY_GET:
 	case AUDIT_TTY_SET:
 	case AUDIT_TRIM:
@@ -1294,6 +1330,7 @@  static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	struct audit_buffer	*ab;
 	u16			msg_type = nlh->nlmsg_type;
 	struct audit_sig_info   *sig_data;
+	struct audit_sig_info2  *sig_data2;
 	char			*ctx = NULL;
 	u32			len;
 
@@ -1559,6 +1596,52 @@  static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 				 sig_data, sizeof(*sig_data) + len);
 		kfree(sig_data);
 		break;
+	case AUDIT_SIGNAL_INFO2: {
+		unsigned int contidstrlen = 0;
+
+		len = 0;
+		if (audit_sig_sid) {
+			err = security_secid_to_secctx(audit_sig_sid, &ctx,
+						       &len);
+			if (err)
+				return err;
+		}
+		if (audit_sig_cid) {
+			contidstr = kmalloc(21, GFP_KERNEL);
+			if (!contidstr) {
+				if (audit_sig_sid)
+					security_release_secctx(ctx, len);
+				return -ENOMEM;
+			}
+			contidstrlen = scnprintf(contidstr, 20, "%llu", audit_sig_cid->id);
+		}
+		sig_data2 = kmalloc(sizeof(*sig_data2) + contidstrlen + len, GFP_KERNEL);
+		if (!sig_data2) {
+			if (audit_sig_sid)
+				security_release_secctx(ctx, len);
+			kfree(contidstr);
+			return -ENOMEM;
+		}
+		sig_data2->uid = from_kuid(&init_user_ns, audit_sig_uid);
+		sig_data2->pid = audit_sig_pid;
+		if (audit_sig_cid) {
+			memcpy(sig_data2->data, contidstr, contidstrlen);
+			sig_data2->cid_len = contidstrlen;
+			kfree(contidstr);
+		}
+		if (audit_sig_sid) {
+			memcpy(sig_data2->data + contidstrlen, ctx, len);
+			security_release_secctx(ctx, len);
+		}
+		rcu_read_lock();
+		_audit_contobj_put_sig(audit_sig_cid);
+		rcu_read_unlock();
+		audit_sig_cid = NULL;
+		audit_send_reply(skb, seq, AUDIT_SIGNAL_INFO2, 0, 0,
+				 sig_data2, sizeof(*sig_data2) + contidstrlen + len);
+		kfree(sig_data2);
+		break;
+	}
 	case AUDIT_TTY_GET: {
 		struct audit_tty_status s;
 		unsigned int t;
@@ -2470,6 +2553,11 @@  int audit_signal_info(int sig, struct task_struct *t)
 		else
 			audit_sig_uid = uid;
 		security_task_getsecid(current, &audit_sig_sid);
+		rcu_read_lock();
+		_audit_contobj_put_sig(audit_sig_cid);
+		audit_sig_cid = _audit_contobj_get_sig(current);
+		rcu_read_unlock();
+		audit_sig_atsk = t;
 	}
 
 	return audit_signal_info_syscall(t);
@@ -2532,6 +2620,11 @@  int audit_set_contid(struct task_struct *task, u64 contid)
 			if (cont->id == contid) {
 				/* task injection to existing container */
 				if (current == cont->owner) {
+					if (!refcount_read(&cont->refcount)) {
+						rc = -ESHUTDOWN;
+						spin_unlock(&audit_contobj_list_lock);
+						goto conterror;
+					}
 					_audit_contobj_hold(cont);
 					newcont = cont;
 				} else {
diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
index b69231918686..8303bb7a63d0 100644
--- a/security/selinux/nlmsgtab.c
+++ b/security/selinux/nlmsgtab.c
@@ -137,6 +137,7 @@  struct nlmsg_perm {
 	{ AUDIT_DEL_RULE,	NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
 	{ AUDIT_USER,		NETLINK_AUDIT_SOCKET__NLMSG_RELAY    },
 	{ AUDIT_SIGNAL_INFO,	NETLINK_AUDIT_SOCKET__NLMSG_READ     },
+	{ AUDIT_SIGNAL_INFO2,	NETLINK_AUDIT_SOCKET__NLMSG_READ     },
 	{ AUDIT_TRIM,		NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
 	{ AUDIT_MAKE_EQUIV,	NETLINK_AUDIT_SOCKET__NLMSG_WRITE    },
 	{ AUDIT_TTY_GET,	NETLINK_AUDIT_SOCKET__NLMSG_READ     },