Take the mmap_read_lock() when using the VMA in
binder_alloc_print_pages() and when checking for a VMA in
binder_alloc_new_buf_locked().
It is worth noting binder_alloc_new_buf_locked() drops the VMA read lock
after it verifies a VMA exists, but may be taken again deeper in the
call stack, if necessary.
Reported-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Reported-by: syzbot+a7b60a176ec13cafb793@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: a43cfc87caaf (android: binder: stop saving a pointer to the VMA)
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
drivers/android/binder_alloc.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index f555eebceef6..c5e7c6d3a844 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -395,12 +395,15 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
size_t size, data_offsets_size;
int ret;
+ mmap_read_lock(alloc->vma_vm_mm);
if (!binder_alloc_get_vma(alloc)) {
+ mmap_read_unlock(alloc->vma_vm_mm);
binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
"%d: binder_alloc_buf, no vma\n",
alloc->pid);
return ERR_PTR(-ESRCH);
}
+ mmap_read_unlock(alloc->vma_vm_mm);
data_offsets_size = ALIGN(data_size, sizeof(void *)) +
ALIGN(offsets_size, sizeof(void *));
@@ -922,17 +925,25 @@ void binder_alloc_print_pages(struct seq_file *m,
* 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++;
- }
+
+ mmap_read_lock(alloc->vma_vm_mm);
+ if (binder_alloc_get_vma(alloc) == NULL) {
+ mmap_read_unlock(alloc->vma_vm_mm);
+ goto uninitialized;
}
+
+ mmap_read_unlock(alloc->vma_vm_mm);
+ 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++;
+ }
+
+uninitialized:
mutex_unlock(&alloc->mutex);
seq_printf(m, " pages: %d:%d:%d\n", active, lru, free);
seq_printf(m, " pages high watermark: %zu\n", alloc->pages_high);
--
2.35.1
