On Sun, Feb 12, 2006 at 12:36:37PM -0700, Matthew Wilcox wrote:
> On Sun, Feb 12, 2006 at 06:06:01PM +0000, Al Viro wrote:
> > On Fri, Feb 10, 2006 at 07:31:07PM -0800, Linda Walsh wrote:
> > > The maximum number of followed symlinks seems to be set to 5.
> > >
> > > This seems small when compared to other filesystem limits.
> > > Is there some objection to it being raised? Should it be
> > > something like Glib's '20' or '255'?
>
> Just a note (which Al probably considered too obvious to point out), but
> MAX_NESTED_LINKS isn't the maximum number of followed symlinks. It's
> the number of recursions we're limited to. The maximum number of
> symlinks followed is 40 (see fs/namei.c:do_follow_link).
>
> Al, would it be worth making 40 an enumerated constant in the same
> enumeration as MAX_NESTED_LINKS? Something like this:
Umm... Maybe. Note that this 40 is to kill very long iterations in
symlinks that are not too deeply nested, but resolving them would
traverse a lot (symlink can have a _lot_ of components - easily as much
as 2048, which leads to 2^55 lookups with depth limited to 5; since
process is unkillable during lookup and it's easy to do a setup where it
wouldn't block on IO...)
IOW, this limit doesn't come from stack overflow concerns - it's just an
arbitrary cutoff point to stop a DoS. We can easily lift it to e.g.
256 if there's any real need. Or make it sysctl-controlled; whatever...
The real hard limit is on nested symlinks.
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