Re: mmap breakage?

On Fri, Apr 02, 2004 at 11:59:57AM -0800, Alfred Perlstein wrote:
> * Poul-Henning Kamp <phk_at_phk.freebsd.dk> [040402 11:14] wrote:
> > In message <20040402191254.GK26131_at_elvis.mu.org>, Alfred Perlstein writes:
> > >* Poul-Henning Kamp <phk_at_phk.freebsd.dk> [040402 10:40] wrote:
> > >> In message <20040402160959.GJ26131_at_elvis.mu.org>, Alfred Perlstein writes:
> > >> >I noticed that mplayer seems to want to open /dev/zero with RDONLY
> > >> >but then tries to mmap it PROT_READ+PROT_WRITE and gets rejected.
> > >> 
> > >> Sounds like missing MAP_PRIVATE ?
> > >
> > >Nope, private is set.  It's just that the file is opened RDONLY,
> > >but PROT has PROT_WRITE in it.
> > 
> > That should be OK with MAP_PRIVATE as far as I interpret POLA.
> 
> Ok, but it's not. :)
 
Alfred,

Please try the attached patch.  This problems appears to be a
consequence of vm/vm_mmap.c revision 1.180, where as part of a much
needed code reorganization for locking the check for the /dev/zero
special case got placed after the permissions check for the general
case.  This patch simply delays the permissions check for devices
until you have the necessary lock to also check for /dev/zero.

Since kan_at_ authored the reorganization, I'm cc:'ing him on this
message for purposes of obtaining a review.  (At least one comment
should be updated to reflect my code changes.)

Regards,
Alan