diff options
| -rw-r--r-- | kernel/seccomp.c | 44 |
1 files changed, 39 insertions, 5 deletions
diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 39c1c687d8ad..ba30bffa9301 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -110,6 +110,14 @@ struct notification { * attached task, once for the dependent filter, and if * requested for the user notifier. When @refs reaches zero, * the filter can be freed. + * @users: A filter's @users count is incremented for each directly + * attached task (filter installation, fork(), thread_sync), + * and once for the dependent filter (tracked in filter->prev). + * When it reaches zero it indicates that no direct or indirect + * users of that filter exist. No new tasks can get associated with + * this filter after reaching 0. The @users count is always smaller + * or equal to @refs. Hence, reaching 0 for @users does not mean + * the filter can be freed. * @log: true if all actions except for SECCOMP_RET_ALLOW should be logged * @prev: points to a previously installed, or inherited, filter * @prog: the BPF program to evaluate @@ -129,6 +137,7 @@ struct notification { */ struct seccomp_filter { refcount_t refs; + refcount_t users; bool log; struct seccomp_filter *prev; struct bpf_prog *prog; @@ -376,6 +385,15 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter) } } +static void __seccomp_filter_orphan(struct seccomp_filter *orig) +{ + while (orig && refcount_dec_and_test(&orig->users)) { + if (waitqueue_active(&orig->wqh)) + wake_up_poll(&orig->wqh, EPOLLHUP); + orig = orig->prev; + } +} + static void __put_seccomp_filter(struct seccomp_filter *orig) { /* Clean up single-reference branches iteratively. */ @@ -386,10 +404,18 @@ static void __put_seccomp_filter(struct seccomp_filter *orig) } } +static void __seccomp_filter_release(struct seccomp_filter *orig) +{ + /* Notify about any unused filters in the task's former filter tree. */ + __seccomp_filter_orphan(orig); + /* Finally drop all references to the task's former tree. */ + __put_seccomp_filter(orig); +} + /** - * seccomp_filter_release - Detach the task from its filter tree - * and drop its reference count during - * exit. + * seccomp_filter_release - Detach the task from its filter tree, + * drop its reference count, and notify + * about unused filters * * This function should only be called when the task is exiting as * it detaches it from its filter tree. As such, READ_ONCE() and @@ -401,7 +427,7 @@ void seccomp_filter_release(struct task_struct *tsk) /* Detach task from its filter tree. */ tsk->seccomp.filter = NULL; - __put_seccomp_filter(orig); + __seccomp_filter_release(orig); } /** @@ -428,12 +454,15 @@ static inline void seccomp_sync_threads(unsigned long flags) /* Get a task reference for the new leaf node. */ get_seccomp_filter(caller); + /* * Drop the task reference to the shared ancestor since * current's path will hold a reference. (This also * allows a put before the assignment.) */ - __put_seccomp_filter(thread->seccomp.filter); + __seccomp_filter_release(thread->seccomp.filter); + + /* Make our new filter tree visible. */ smp_store_release(&thread->seccomp.filter, caller->seccomp.filter); atomic_set(&thread->seccomp.filter_count, @@ -502,6 +531,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) } refcount_set(&sfilter->refs, 1); + refcount_set(&sfilter->users, 1); init_waitqueue_head(&sfilter->wqh); return sfilter; @@ -606,6 +636,7 @@ void get_seccomp_filter(struct task_struct *tsk) if (!orig) return; __get_seccomp_filter(orig); + refcount_inc(&orig->users); } static void seccomp_init_siginfo(kernel_siginfo_t *info, int syscall, int reason) @@ -1234,6 +1265,9 @@ static __poll_t seccomp_notify_poll(struct file *file, mutex_unlock(&filter->notify_lock); + if (refcount_read(&filter->users) == 0) + ret |= EPOLLHUP; + return ret; } |