svn commit: r192094 - head/sys/kern

[Ed Schouten]

Hi Kostik,

* Konstantin Belousov <kib at 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.

-- 
 Ed Schouten <ed at 80386.nl>
 WWW: http://80386.nl/
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