From 8eb52a1ee37aafd9b796713aa0b3ab9cbc455be3 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Fri, 18 Oct 2019 22:56:29 +0200 Subject: binder: Fix race between mmap() and binder_alloc_print_pages() binder_alloc_print_pages() iterates over alloc->pages[0..alloc->buffer_size-1] under alloc->mutex. binder_alloc_mmap_handler() writes alloc->pages and alloc->buffer_size without holding that lock, and even writes them before the last bailout point. Unfortunately we can't take the alloc->mutex in the ->mmap() handler because mmap_sem can be taken while alloc->mutex is held. So instead, we have to locklessly check whether the binder_alloc has been fully initialized with binder_alloc_get_vma(), like in binder_alloc_new_buf_locked(). Fixes: 8ef4665aa129 ("android: binder: Add page usage in binder stats") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Acked-by: Christian Brauner Link: https://lore.kernel.org/r/20191018205631.248274-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) (limited to 'drivers/android') diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 1cbe37823de2..d718ed0537be 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -840,14 +840,20 @@ void binder_alloc_print_pages(struct seq_file *m, int free = 0; mutex_lock(&alloc->mutex); - for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) { - page = &alloc->pages[i]; - if (!page->page_ptr) - free++; - else if (list_empty(&page->lru)) - active++; - else - lru++; + /* + * Make sure the binder_alloc is fully initialized, otherwise we might + * read inconsistent state. + */ + if (binder_alloc_get_vma(alloc) != NULL) { + for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) { + page = &alloc->pages[i]; + if (!page->page_ptr) + free++; + else if (list_empty(&page->lru)) + active++; + else + lru++; + } } mutex_unlock(&alloc->mutex); seq_printf(m, " pages: %d:%d:%d\n", active, lru, free); -- cgit v1.2.3