On Tue, Aug 30, 2022 at 07:06:37PM +0000, Liam Howlett wrote:
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 51f4e1c5cd01..9b1778c00610 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -322,7 +322,6 @@ static inline void binder_alloc_set_vma(struct binder_alloc *alloc, */ if (vma) { vm_start = vma->vm_start;
alloc->vma_vm_mm = vma->vm_mm;Is this really the null pointer dereference? We check for vma above..?
Not here. The sequence leading to the null-ptr-deref happens when we try to take alloc->vma_vm_mm->mmap_lock in binder_alloc_new_buf_locked() and in binder_alloc_print_pages() without initializing alloc->vma_vm_mm first (e.g. mmap() was never called). These sequences are described in the commit message but basically they translate to mmap_read_lock(NULL) calls.