Re: [PATCH ghak90 V9 06/13] audit: add contid support for signalling the audit daemon

On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb(a)redhat.com&gt; 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(a)redhat.com&gt; > --- > 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