On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > Implement the proc fs write to set the audit container identifier of a > process, emitting an AUDIT_CONTAINER_OP record to document the event. > > This is a write from the container orchestrator task to a proc entry of > the form /proc/PID/audit_containerid where PID is the process ID of the > newly created task that is to become the first task in a container, or > an additional task added to a container. > > The write expects up to a u64 value (unset: 18446744073709551615). > > The writer must have capability CAP_AUDIT_CONTROL. > > This will produce a record such as this: > type=CONTAINER_OP msg=audit(2018-06-06 12:39:29.636:26949) : op=set opid=2209 contid=123456 old-contid=18446744073709551615 > > The "op" field indicates an initial set. The "opid" field is the > object's PID, the process being "contained". New and old audit > container identifier values are given in the "contid" fields. > > It is not permitted to unset the audit container identifier. > A child inherits its parent's audit container identifier. > > Store the audit container identifier in a refcounted kernel object that > is added to the master list of audit container identifiers. This will > allow multiple container orchestrators/engines to work on the same > machine without danger of inadvertantly re-using an existing identifier. > It will also allow an orchestrator to inject a process into an existing > container by checking if the original container owner is the one > injecting the task. A hash table list is used to optimize searches. > > Please see the github audit kernel issue for the main feature: > https://github.com/linux-audit/audit-kernel/issues/90 > Please see the github audit userspace issue for supporting additions: > https://github.com/linux-audit/audit-userspace/issues/51 > Please see the github audit testsuiite issue for the test case: > https://github.com/linux-audit/audit-testsuite/issues/64 > Please see the github audit wiki for the feature overview: > https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID > > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx> > Acked-by: Serge Hallyn <serge@xxxxxxxxxx> > Acked-by: Steve Grubb <sgrubb@xxxxxxxxxx> > Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx> > Reviewed-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx> > --- > fs/proc/base.c | 36 +++++++++++ > include/linux/audit.h | 33 ++++++++++ > include/uapi/linux/audit.h | 2 + > kernel/audit.c | 148 +++++++++++++++++++++++++++++++++++++++++++++ > kernel/audit.h | 8 +++ > 5 files changed, 227 insertions(+) ... > diff --git a/include/linux/audit.h b/include/linux/audit.h > index c2150415f9df..2800d4f1a2a8 100644 > --- a/include/linux/audit.h > +++ b/include/linux/audit.h > @@ -692,6 +715,16 @@ static inline bool audit_loginuid_set(struct task_struct *tsk) > return uid_valid(audit_get_loginuid(tsk)); > } > > +static inline bool audit_contid_valid(u64 contid) > +{ > + return contid != AUDIT_CID_UNSET; > +} > + > +static inline bool audit_contid_set(struct task_struct *tsk) > +{ > + return audit_contid_valid(audit_get_contid(tsk)); > +} This is quasi-nitpicky, but it seems like audit_contid_valid() and audit_contid_set() should be moved to kernel/audit.h if possible (possibly even kernel/audit.c). Maybe I'll see something later in the patchset, but right now I'm struggling to think of why anyone outside of audit would need to call these functions. > diff --git a/kernel/audit.c b/kernel/audit.c > index 5d8147a29291..6d387793f702 100644 > --- a/kernel/audit.c > +++ b/kernel/audit.c > @@ -138,6 +138,13 @@ struct auditd_connection { > > /* Hash for inode-based rules */ > struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS]; > +/* Hash for contid object lists */ > +struct list_head audit_contid_hash[AUDIT_CONTID_BUCKETS]; > +/* Lock all additions and deletions to the contid hash lists, assignment > + * of container objects to tasks. There should be no need for > + * interaction with tasklist_lock > + */ > +static DEFINE_SPINLOCK(audit_contobj_list_lock); > > static struct kmem_cache *audit_buffer_cache; > > @@ -212,6 +219,33 @@ void __init audit_task_init(void) > 0, SLAB_PANIC, NULL); > } > > +/* rcu_read_lock must be held by caller unless new */ > +static struct audit_contobj *_audit_contobj_hold(struct audit_contobj *cont) > +{ > + if (cont) > + refcount_inc(&cont->refcount); > + return cont; > +} > + > +static struct audit_contobj *_audit_contobj_get(struct task_struct *tsk) > +{ > + if (!tsk->audit) > + return NULL; > + return _audit_contobj_hold(tsk->audit->cont); > +} > + > +/* rcu_read_lock must be held by caller */ > +static void _audit_contobj_put(struct audit_contobj *cont) > +{ > + if (!cont) > + return; > + if (refcount_dec_and_test(&cont->refcount)) { > + put_task_struct(cont->owner); > + list_del_rcu(&cont->list); You should check your locking; I'm used to seeing exclusive locks (e.g. the spinlock) around list adds/removes, it just reads/traversals that can be done with just the RCU lock held. > + kfree_rcu(cont, rcu); > + } > +} Another nitpick, but it might be nice to have similar arguments to the _get() and _put() functions, e.g. struct audit_contobj, but that is some serious bikeshedding (basically rename _hold() to _get() and rename _hold to audit_task_contid_hold() or similar). > /** > * audit_alloc - allocate an audit info block for a task > * @tsk: task > @@ -232,6 +266,9 @@ int audit_alloc(struct task_struct *tsk) > } > info->loginuid = audit_get_loginuid(current); > info->sessionid = audit_get_sessionid(current); > + rcu_read_lock(); > + info->cont = _audit_contobj_get(current); > + rcu_read_unlock(); The RCU locks aren't strictly necessary here, are they? In fact I suppose we could probably just replace the _get() call with a refcount_set(1) just as we do in audit_set_contid(), yes? > tsk->audit = info; > > ret = audit_alloc_syscall(tsk); > @@ -246,6 +283,7 @@ int audit_alloc(struct task_struct *tsk) > struct audit_task_info init_struct_audit = { > .loginuid = INVALID_UID, > .sessionid = AUDIT_SID_UNSET, > + .cont = NULL, > #ifdef CONFIG_AUDITSYSCALL > .ctx = NULL, > #endif > @@ -262,6 +300,9 @@ void audit_free(struct task_struct *tsk) > struct audit_task_info *info = tsk->audit; > > audit_free_syscall(tsk); > + rcu_read_lock(); > + _audit_contobj_put(tsk->audit->cont); > + rcu_read_unlock(); > /* Freeing the audit_task_info struct must be performed after > * audit_log_exit() due to need for loginuid and sessionid. > */ > @@ -1709,6 +1750,9 @@ static int __init audit_init(void) > for (i = 0; i < AUDIT_INODE_BUCKETS; i++) > INIT_LIST_HEAD(&audit_inode_hash[i]); > > + for (i = 0; i < AUDIT_CONTID_BUCKETS; i++) > + INIT_LIST_HEAD(&audit_contid_hash[i]); > + > mutex_init(&audit_cmd_mutex.lock); > audit_cmd_mutex.owner = NULL; > > @@ -2410,6 +2454,110 @@ int audit_signal_info(int sig, struct task_struct *t) > return audit_signal_info_syscall(t); > } > > +/* > + * audit_set_contid - set current task's audit contid > + * @task: target task > + * @contid: contid value > + * > + * Returns 0 on success, -EPERM on permission failure. > + * > + * If the original container owner goes away, no task injection is > + * possible to an existing container. > + * > + * Called (set) from fs/proc/base.c::proc_contid_write(). > + */ > +int audit_set_contid(struct task_struct *task, u64 contid) > +{ > + int rc = 0; > + struct audit_buffer *ab; > + struct audit_contobj *oldcont = NULL; > + > + task_lock(task); > + /* Can't set if audit disabled */ > + if (!task->audit) { > + task_unlock(task); > + return -ENOPROTOOPT; > + } See my question/comment in patch 1/13; this check may not be needed or it may need to be changed to something other than "!task->audit". > + read_lock(&tasklist_lock); > + /* Don't allow the contid to be unset */ > + if (!audit_contid_valid(contid)) { > + rc = -EINVAL; > + goto unlock; > + } > + /* if we don't have caps, reject */ > + if (!capable(CAP_AUDIT_CONTROL)) { > + rc = -EPERM; > + goto unlock; > + } > + /* if task has children or is not single-threaded, deny */ > + if (!list_empty(&task->children) || > + !(thread_group_leader(task) && thread_group_empty(task))) { > + rc = -EBUSY; > + goto unlock; > + } > + /* if contid is already set, deny */ > + if (audit_contid_set(task)) > + rc = -EEXIST; > +unlock: Can we move the "unlock" target to the end of the function where it just handles the unlocking and returns an error, including the AUDIT_CONTAINER_OP record if necessary? From what I can see we only jump to "unlock" in case of error where we are not going to set the audit container ID, yet the "unlock" target is placed in a misleading location in the middle of the function. It may be that everything works correctly, but I would argue this is a bad practice that increases the likelihood of buggy behavior in future code changes. If you can't find way to arrange the code nicely, just duplicate the "tasklist_lock" unlock operation in the error handlers before jumping down to the end of the function. It isn't perfect, but I believe it will be a lot less fragile than the current approach. > + read_unlock(&tasklist_lock); > + rcu_read_lock(); > + oldcont = _audit_contobj_get(task); > + if (!rc) { > + struct audit_contobj *cont = NULL, *newcont = NULL; > + int h = audit_hash_contid(contid); > + > + spin_lock(&audit_contobj_list_lock); > + list_for_each_entry_rcu(cont, &audit_contid_hash[h], list) > + if (cont->id == contid) { > + /* task injection to existing container */ > + if (current == cont->owner) { > + _audit_contobj_hold(cont); > + newcont = cont; > + } else { > + rc = -ENOTUNIQ; > + spin_unlock(&audit_contobj_list_lock); > + goto conterror; > + } > + break; > + } > + if (!newcont) { > + newcont = kmalloc(sizeof(*newcont), GFP_ATOMIC); > + if (newcont) { > + INIT_LIST_HEAD(&newcont->list); > + newcont->id = contid; > + newcont->owner = get_task_struct(current); > + refcount_set(&newcont->refcount, 1); > + list_add_rcu(&newcont->list, > + &audit_contid_hash[h]); > + } else { > + rc = -ENOMEM; > + spin_unlock(&audit_contobj_list_lock); > + goto conterror; > + } > + } > + spin_unlock(&audit_contobj_list_lock); > + task->audit->cont = newcont; > + _audit_contobj_put(oldcont); > + } > +conterror: > + task_unlock(task); > + > + if (!audit_enabled) > + return rc; > + > + ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONTAINER_OP); > + if (!ab) > + return rc; > + > + audit_log_format(ab, > + "op=set opid=%d contid=%llu old-contid=%llu", > + task_tgid_nr(task), contid, oldcont ? oldcont->id : -1); > + _audit_contobj_put(oldcont); > + rcu_read_unlock(); > + audit_log_end(ab); > + return rc; > +} -- paul moore www.paul-moore.com
