vm_ops->fault may be called in parallel. Because we have to resort to temporarily changing the vma->vm_file to point to the lower file, a concurrent invocation of unionfs_fault could see a different value. In this workaround, we keep a different copy of the vma structure in our stack, so we never expose a different value of the vma->vm_file called to us, even temporarily. A better fix (already tested) would be to change the calling semantics of ->fault to take an explicit file pointer. Signed-off-by: Erez Zadok <ezk@xxxxxxxxxxxxx> --- fs/unionfs/mmap.c | 21 +++++++++++++-------- 1 files changed, 13 insertions(+), 8 deletions(-) diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c index 07db5b0..febde7c 100644 --- a/fs/unionfs/mmap.c +++ b/fs/unionfs/mmap.c @@ -40,23 +40,28 @@ static int unionfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf) int err; struct file *file, *lower_file; struct vm_operations_struct *lower_vm_ops; + struct vm_area_struct lower_vma; BUG_ON(!vma); - file = vma->vm_file; + memcpy(&lower_vma, vma, sizeof(struct vm_area_struct)); + file = lower_vma.vm_file; lower_vm_ops = UNIONFS_F(file)->lower_vm_ops; BUG_ON(!lower_vm_ops); lower_file = unionfs_lower_file(file); BUG_ON(!lower_file); /* - * XXX: we set the vm_file to the lower_file, before calling the - * lower ->fault op, then we restore the vm_file back to the upper - * file. Need to change the ->fault prototype to take an explicit - * struct file, and fix all users accordingly. + * XXX: vm_ops->fault may be called in parallel. Because we have to + * resort to temporarily changing the vma->vm_file to point to the + * lower file, a concurrent invocation of unionfs_fault could see a + * different value. In this workaround, we keep a different copy of + * the vma structure in our stack, so we never expose a different + * value of the vma->vm_file called to us, even temporarily. A + * better fix would be to change the calling semantics of ->fault to + * take an explicit file pointer. */ - vma->vm_file = lower_file; - err = lower_vm_ops->fault(vma, vmf); - vma->vm_file = file; + lower_vma.vm_file = lower_file; + err = lower_vm_ops->fault(&lower_vma, vmf); return err; } -- 1.5.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
