Re: [PATCH] fadvise: avoid EINVAL if user input is valid

[Eric Wong <normalperson@yhbt.net>]

Hillf Danton <dhillf@gmail.com> wrote:
> On Sat, Feb 25, 2012 at 10:27 AM, Eric Wong <normalperson@yhbt.net> wrote:
> > index 469491e0..f9e48dd 100644
> > --- a/mm/fadvise.c
> > +++ b/mm/fadvise.c
> > @@ -43,13 +43,13 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
> > A  A  A  A  A  A  A  A goto out;
> > A  A  A  A }
> >
> > - A  A  A  mapping = file->f_mapping;
> > - A  A  A  if (!mapping || len < 0) {
> > + A  A  A  if (len < 0) {
> 
> Current code makes sure mapping is valid after the above check,

Right.  I moved the !mapping check down a few lines.

> > A  A  A  A  A  A  A  A ret = -EINVAL;
> > A  A  A  A  A  A  A  A goto out;
> > A  A  A  A }

Now the check hits the "goto out" the get_xip_mem check hits:

> > - A  A  A  if (mapping->a_ops->get_xip_mem) {
> > + A  A  A  mapping = file->f_mapping;
> > + A  A  A  if (!mapping || mapping->a_ops->get_xip_mem) {
> > A  A  A  A  A  A  A  A switch (advice) {
> > A  A  A  A  A  A  A  A case POSIX_FADV_NORMAL:
> > A  A  A  A  A  A  A  A case POSIX_FADV_RANDOM:

		case POSIX_FADV_SEQUENTIAL:
		case POSIX_FADV_WILLNEED:
		case POSIX_FADV_NOREUSE:
		case POSIX_FADV_DONTNEED:
			/* no bad return value, but ignore advice */
			break;
		default:
			ret = -EINVAL;
		}
		goto out; <------ we hit this if (mapping == NULL)
	}

> but backing devices info is no longer evaluated with that
> guarantee in your change.
> 
> -hd
> 
> 75:	bdi = mapping->backing_dev_info;

The above line still doesn't evaluated because of the goto.

out:
	fput(file);
	return ret;
}

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