I need to make a change to this patch, so please ignore this version.
I'll send a v2 soon.
On Thu, Dec 13, 2018 at 1:04 PM Todd Kjos <tkjos@xxxxxxxxxxx> wrote:
>
> 44d8047f1d8 ("binder: use standard functions to allocate fds")
> exposed a pre-existing issue in the binder driver.
>
> fdget() is used in ksys_ioctl() as a performance optimization.
> One of the rules associated with fdget() is that ksys_close() must
> not be called between the fdget() and the fdput(). There is a case
> where this requirement is not met in the binder driver which results
> in the reference count dropping to 0 when the device is still in
> use. This can result in use-after-free or other issues.
>
> If userpace has passed a file-descriptor for the binder driver using
> a BINDER_TYPE_FDA object, then kys_close() is called on it when
> handling a binder_ioctl(BC_FREE_BUFFER) command. This violates
> the assumptions for using fdget().
>
> The problem is fixed by deferring the fd close using task_work_add()
> so ksys_close() is called after returning from binder_ioctl().
>
> Fixes: 44d8047f1d87a ("binder: use standard functions to allocate fds")
> Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx>
> ---
> drivers/android/binder.c | 91 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 81 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index c525b164d39d2..8f77d6af31209 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -72,6 +72,7 @@
> #include <linux/spinlock.h>
> #include <linux/ratelimit.h>
> #include <linux/syscalls.h>
> +#include <linux/task_work.h>
>
> #include <uapi/linux/android/binder.h>
>
> @@ -560,6 +561,9 @@ enum {
> * (protected by @proc->inner_lock)
> * @waiting_thread_node: element for @proc->waiting_threads list
> * (protected by @proc->inner_lock)
> + * @deferred_close_fd_cb: callback_head for task work
> + * @deferred_close_fds: list of fds to be closed
> + * (only accessed by this thread)
> * @pid: PID for this thread
> * (invariant after initialization)
> * @looper: bitmap of looping state
> @@ -592,6 +596,8 @@ struct binder_thread {
> struct binder_proc *proc;
> struct rb_node rb_node;
> struct list_head waiting_thread_node;
> + struct callback_head deferred_close_fd_cb;
> + struct hlist_head deferred_close_fds;
> int pid;
> int looper; /* only modified by this thread */
> bool looper_need_return; /* can be written by other thread */
> @@ -2184,7 +2190,64 @@ static bool binder_validate_fixup(struct binder_buffer *b,
> return (fixup_offset >= last_min_offset);
> }
>
> +struct binder_task_work {
> + struct hlist_node entry;
> + int fd;
> +};
> +
> +/**
> + * binder_do_fd_close() - close list of file descriptors
> + * @twork: callback head for task work
> + *
> + * It is not safe to call ksys_close() during the binder_ioctl()
> + * function if there is a chance that binder's own file descriptor
> + * might be closed. This is to meet the requirements for using
> + * fdget() (see comments for __fget_light()). Therefore use
> + * task_add_work() to schedule the close operation once we have
> + * returned from binder_ioctl(). This function is a callback
> + * for that mechanism and does the actual ksys_close() on the list
> + * of file descriptors.
> + */
> +static void binder_do_fd_close(struct callback_head *twork)
> +{
> + struct binder_thread *thread = container_of(twork,
> + struct binder_thread, deferred_close_fd_cb);
> + struct hlist_node *entry, *tmp;
> +
> + hlist_for_each_safe(entry, tmp, &thread->deferred_close_fds) {
> + struct binder_task_work *work = container_of(entry,
> + struct binder_task_work, entry);
> +
> + ksys_close(work->fd);
> + hlist_del(&work->entry);
> + kfree(work);
> + }
> +}
> +
> +/**
> + * binder_deferred_fd_close() - schedule a close for the given file-descriptor
> + * @thread: struct binder_thread for this task
> + * @fd: file-descriptor to close
> + *
> + * See comments in binder_do_fd_close(). This function is used to schedule
> + * a file-descriptor to be closed after returning from binder_ioctl().
> + */
> +static void binder_deferred_fd_close(struct binder_thread *thread, int fd)
> +{
> + struct binder_task_work *work;
> +
> + work = kzalloc(sizeof(*work), GFP_KERNEL);
> + if (!work)
> + return;
> + work->fd = fd;
> +
> + if (hlist_empty(&thread->deferred_close_fds))
> + task_work_add(current, &thread->deferred_close_fd_cb, true);
> + hlist_add_head(&work->entry, &thread->deferred_close_fds);
> +}
> +
> static void binder_transaction_buffer_release(struct binder_proc *proc,
> + struct binder_thread *thread,
> struct binder_buffer *buffer,
> binder_size_t *failed_at)
> {
> @@ -2323,7 +2386,8 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
> }
> fd_array = (u32 *)(parent_buffer + (uintptr_t)fda->parent_offset);
> for (fd_index = 0; fd_index < fda->num_fds; fd_index++)
> - ksys_close(fd_array[fd_index]);
> + binder_deferred_fd_close(thread,
> + fd_array[fd_index]);
> } break;
> default:
> pr_err("transaction release %d bad object type %x\n",
> @@ -3266,7 +3330,7 @@ static void binder_transaction(struct binder_proc *proc,
> err_copy_data_failed:
> binder_free_txn_fixups(t);
> trace_binder_transaction_failed_buffer_release(t->buffer);
> - binder_transaction_buffer_release(target_proc, t->buffer, offp);
> + binder_transaction_buffer_release(target_proc, thread, t->buffer, offp);
> if (target_node)
> binder_dec_node_tmpref(target_node);
> target_node = NULL;
> @@ -3330,6 +3394,7 @@ static void binder_transaction(struct binder_proc *proc,
> /**
> * binder_free_buf() - free the specified buffer
> * @proc: binder proc that owns buffer
> + * @thread: current binder thread
> * @buffer: buffer to be freed
> *
> * If buffer for an async transaction, enqueue the next async
> @@ -3338,7 +3403,8 @@ static void binder_transaction(struct binder_proc *proc,
> * Cleanup buffer and free it.
> */
> static void
> -binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer)
> +binder_free_buf(struct binder_proc *proc, struct binder_thread *thread,
> + struct binder_buffer *buffer)
> {
> if (buffer->transaction) {
> buffer->transaction->buffer = NULL;
> @@ -3364,7 +3430,7 @@ binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer)
> binder_node_inner_unlock(buf_node);
> }
> trace_binder_transaction_buffer_release(buffer);
> - binder_transaction_buffer_release(proc, buffer, NULL);
> + binder_transaction_buffer_release(proc, thread, buffer, NULL);
> binder_alloc_free_buf(&proc->alloc, buffer);
> }
>
> @@ -3558,7 +3624,7 @@ static int binder_thread_write(struct binder_proc *proc,
> proc->pid, thread->pid, (u64)data_ptr,
> buffer->debug_id,
> buffer->transaction ? "active" : "finished");
> - binder_free_buf(proc, buffer);
> + binder_free_buf(proc, thread, buffer);
> break;
> }
>
> @@ -3883,7 +3949,8 @@ static int binder_wait_for_work(struct binder_thread *thread,
>
> /**
> * binder_apply_fd_fixups() - finish fd translation
> - * @t: binder transaction with list of fd fixups
> + * @thread: current binder thread
> + * @t: binder transaction with list of fd fixups
> *
> * Now that we are in the context of the transaction target
> * process, we can allocate and install fds. Process the
> @@ -3894,7 +3961,8 @@ static int binder_wait_for_work(struct binder_thread *thread,
> * fput'ing files that have not been processed and ksys_close'ing
> * any fds that have already been allocated.
> */
> -static int binder_apply_fd_fixups(struct binder_transaction *t)
> +static int binder_apply_fd_fixups(struct binder_thread *thread,
> + struct binder_transaction *t)
> {
> struct binder_txn_fd_fixup *fixup, *tmp;
> int ret = 0;
> @@ -3942,7 +4010,7 @@ static int binder_apply_fd_fixups(struct binder_transaction *t)
> } else if (ret) {
> u32 *fdp = (u32 *)(t->buffer->data + fixup->offset);
>
> - ksys_close(*fdp);
> + binder_deferred_fd_close(thread, *fdp);
> }
> list_del(&fixup->fixup_entry);
> kfree(fixup);
> @@ -4237,7 +4305,7 @@ static int binder_thread_read(struct binder_proc *proc,
> tr.sender_pid = 0;
> }
>
> - ret = binder_apply_fd_fixups(t);
> + ret = binder_apply_fd_fixups(thread, t);
> if (ret) {
> struct binder_buffer *buffer = t->buffer;
> bool oneway = !!(t->flags & TF_ONE_WAY);
> @@ -4248,7 +4316,7 @@ static int binder_thread_read(struct binder_proc *proc,
> buffer->transaction = NULL;
> binder_cleanup_transaction(t, "fd fixups failed",
> BR_FAILED_REPLY);
> - binder_free_buf(proc, buffer);
> + binder_free_buf(proc, thread, buffer);
> binder_debug(BINDER_DEBUG_FAILED_TRANSACTION,
> "%d:%d %stransaction %d fd fixups failed %d/%d, line %d\n",
> proc->pid, thread->pid,
> @@ -4433,6 +4501,8 @@ static struct binder_thread *binder_get_thread_ilocked(
> thread->reply_error.work.type = BINDER_WORK_RETURN_ERROR;
> thread->reply_error.cmd = BR_OK;
> INIT_LIST_HEAD(&new_thread->waiting_thread_node);
> + INIT_HLIST_HEAD(&new_thread->deferred_close_fds);
> + init_task_work(&new_thread->deferred_close_fd_cb, binder_do_fd_close);
> return thread;
> }
>
> @@ -4470,6 +4540,7 @@ static void binder_free_proc(struct binder_proc *proc)
> static void binder_free_thread(struct binder_thread *thread)
> {
> BUG_ON(!list_empty(&thread->todo));
> + BUG_ON(!hlist_empty(&thread->deferred_close_fds));
> binder_stats_deleted(BINDER_STAT_THREAD);
> binder_proc_dec_tmpref(thread->proc);
> kfree(thread);
> --
> 2.20.0.rc2.403.gdbc3b29805-goog
>
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