Re: [PATCH v5 0/3] close_range()

[Christian Brauner <christian.brauner@ubuntu.com>]

On Wed, Jun 03, 2020 at 05:13:36PM -0700, Linus Torvalds wrote:
> On Wed, Jun 3, 2020 at 4:24 PM Christian Brauner
> <christian.brauner@ubuntu.com> wrote:
> >
> > Ok, here's what I have. Does the below look somewhat sane?
> 
> Probably. Needs lots of testing. But this one looks wrong:

Right, there's a patch for a test-suite for the new flag too using
CLONE_FILES to create a shared fdtable and the proceeds to close all
(or subsets of) fds:

https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/commit/?h=close_range&id=498e7e844fe6e3f3306b2cd1b5e926e1cd394b99

I've been running that in an endless loop for a while.

> 
> > +int __close_range(unsigned fd, unsigned max_fd, unsigned int flags)
> >  {
> > +               if ((max_fd + 1) >= cur_max)
> > +                       max_unshare_fds = fd;
> 
> A normal value for "close everything starting at X" would have a
> max_fd value of ~0.

Ugh, obvious braino from my side. This should just be:

if (max_fd >= cur_max)
	max_unshare_fds = fd;

> 
> So "max_fd+1" would overflow to 0, and then this would never trigger.
> 
> Other than that it looks what what I imagine my feverdreams were about.

Thanks!
Christian