diff options
author | Jann Horn <jannh@google.com> | 2019-10-18 22:56:29 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-11-14 11:44:46 +0800 |
commit | 8eb52a1ee37aafd9b796713aa0b3ab9cbc455be3 (patch) | |
tree | 5263874068ffdda554cdb83c897728299b898d9d | |
parent | 60f8a59ddcdc7fb7c17180ba10d9c49bc91156c7 (diff) | |
download | linux-next-8eb52a1ee37aafd9b796713aa0b3ab9cbc455be3.tar.gz |
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 <jannh@google.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191018205631.248274-1-jannh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | drivers/android/binder_alloc.c | 22 |
1 files changed, 14 insertions, 8 deletions
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); |