Re: [PATCH] proc: advertise new restrictions on /proc/*/maps & /proc/*/smaps

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Jan 04, 2008 at 12:15:02PM +0100, Guillaume Chazarain wrote:
> Al Viro <viro@ZenIV.linux.org.uk> wrote:
> 
> > The whole point is that we have to reject it at read() time, not open()
> > time.
> 
> Yes, my patch was a complement to yours to propagate the -EPERM in easy
> cases. As you noted it added restrictions on reading /proc/*/maps, even
> though I found them acceptable.
> 
> How about this instead?
> 
> Maybe you'd prefer to propagate the actual -EPERM from
> __ptrace_may_attach but that would be more invasive.
> 
> Sidenote: do you think a sparse annotation to check IS_ERR/PTR_ERR
> usage would make sense?
> 
> proc: return -EPERM when preventing read of /proc/*/maps
> 
> Return an error instead of successfully reading an empty file.

You are overcomplicating it - if ->start() returns ERR_PTR(), it's over;
read() will fail with that error and that's it.  No need to mess with
->next(), etc. - it'll never see that ERR_PTR(-EPERM).  Drop these chunks
and you've got an ACK...