On Fri, May 15, 2009 at 10:06:13AM +0200, Peter Holm wrote:
> On Fri, May 15, 2009 at 09:02:39AM +0200, Ed Schouten wrote:
> > Hi Kostik,
> >
> > * Konstantin Belousov <k...@freebsd.org> wrote:
> > > Log:
> > > Do not advance req->oldidx when sysctl_old_user returning an
> > > error due to copyout failure or short buffer.
> > >
> > > The later breaks the usermode iterators of the sysctl results that pack
> > > arbitrary number of variable-sized structures. Iterator expects that
> > > kernel filled exactly oldlen bytes, and tries to interpret half-filled
> > > or garbage structure at the end of the buffer. In particular,
> > > kinfo_getfile(3) segfaulted.
> > >
> > > Reported and tested by: pho
> > > MFC after: 3 weeks
> >
> > Is it possible that this change introduces a regression? Right now
> > `pstat -t' gets stuck in an infinite loop. I've added the following
> > printf:
> >
> > | Index: pstat.c
> > | ===================================================================
> > | --- pstat.c (revision 192128)
> > | +++ pstat.c (working copy)
> > | @@ -263,6 +263,7 @@
> > | if (errno != ENOMEM)
> > | err(1, "sysctlbyname()");
> > | len *= 2;
> > | + printf("Going to %zu\n", len);
> > | if ((xttys = realloc(xttys, len)) == NULL)
> > | err(1, "realloc()");
> > | }
> >
> > pstat on -CURRENT prints:
> >
> > | LINE INQ CAN LIN LOW OUTQ USE LOW COL SESS PGID STATE
> > | Going to 0
> > | Going to 0
> > | Going to 0
> > | ...
> >
> > If I use the same patch on RELENG_6, I get the expected result:
> >
> > | LINE RAW CAN OUT IHIWT ILOWT OHWT LWT COL STATE SESS PGID
> > DISC
> > | Going to 272
> > | Going to 544
> > | Going to 1088
> > | Going to 2176
> > | Going to 4352
> > | Going to 8704
> > | sysmouse 0 0 0 0 0 0 0 0 - 0 0
> > term
> > | ...
> >
> > So the problem is that sysctl overwrites the len argument with 0, even
> > if it returns back to userspace with ENOMEM.
> >
> > I see we have two changes in sysctl. In theory it could also be related
> > to jhb@'s changes to sysctl locking, but I suspect it's less likely.
> >
>
> I can confirm that it is r192094 that triggers the loop.Yes, this is what I mean when talked about a breakage. Below is the reversal of r192094 + the change to keep the old, ugly behaviour of sysctl kern.proc.filedesc to return 0 on ENOMEM, but with oldlen chopped at the end of the last completely written struct kern_info instead of the middle of partially-written one. Peter, could you, please, retest ?
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