Re: Hard lock when mounting loopback file

[Andrew Morton]

Marius Gedminas wrote:
> 
> On Sat, Jan 12, 2002 at 11:49:04PM -0800, Andrew Morton wrote:
> > I don't know a thing about fat layout, but it appears that it uses a
> > linked list of blocks, and if that list ends up pointing back onto
> > itself, the kernel goes into an infinite loop in several places chasing
> > its way to the end of the list.
> >
> > The below patch fixed it for me, and I was able to mount and read
> > your filesystem image.
> >
> > Unless someone has a smarter fix, I'll send this to the kernel
> > maintainers in a week or two.
> 
> It seems to me that this patch will find only those infinite loops where
> the last link of the chain points to itself.  But there could be loops
> where the last link points to the middle of the chain.

Agree.

> Additional check on the number of followed links could be useful there.
> No chain should be longer than the number of clusters on the fs.
> Although on large FAT32 filesystems the number of clusters can be high,
> a very long loop is still better than an infinite one.  (In cases where
> we know the file size, this limit can be reduced to
> file_size/cluster_size + 1 links).

hmm..  OK, I'll take a look at that approach.

-