On Fri, May 15, 2009 at 12:48:52PM +0300, Kostik Belousov wrote:
> 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 ?
Err, the patch.
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index f29b0eb..e0008e6 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2883,6 +2883,7 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
struct proc *p;
struct tty *tp;
int vfslocked;
+ size_t oldidx;
name = (int *)arg1;
if ((p = pfind((pid_t)name[0])) == NULL)
@@ -3061,14 +3062,26 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
strlen(kif->kf_path) + 1;
kif->kf_structsize = roundup(kif->kf_structsize,
sizeof(uint64_t));
+ oldidx = req->oldidx;
error = SYSCTL_OUT(req, kif, kif->kf_structsize);
- if (error)
+ if (error) {
+ if (error == ENOMEM) {
+ /*
+ * The hack to keep the ABI of sysctl
+ * kern.proc.filedesc intact, but not
+ * to account a partially copied
+ * kinfo_file into the oldidx.
+ */
+ req->oldidx = oldidx;
+ error = 0;
+ }
break;
+ }
}
FILEDESC_SUNLOCK(fdp);
fddrop(fdp);
free(kif, M_TEMP);
- return (0);
+ return (error);
}
static SYSCTL_NODE(_kern_proc, KERN_PROC_FILEDESC, filedesc, CTLFLAG_RD,
diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index bf539be..0a8a096 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -1223,9 +1223,9 @@ sysctl_old_kernel(struct sysctl_req *req, const void *p,
size_t l)
if (i > 0)
bcopy(p, (char *)req->oldptr + req->oldidx, i);
}
+ req->oldidx += l;
if (req->oldptr && i != l)
return (ENOMEM);
- req->oldidx += l;
return (0);
}
@@ -1322,10 +1322,9 @@ sysctl_old_user(struct sysctl_req *req, const void *p,
size_t l)
size_t i, len, origidx;
origidx = req->oldidx;
- if (req->oldptr == NULL) {
- req->oldidx += l;
+ req->oldidx += l;
+ if (req->oldptr == NULL)
return (0);
- }
/*
* If we have not wired the user supplied buffer and we are currently
* holding locks, drop a witness warning, as it's possible that
@@ -1347,7 +1346,6 @@ sysctl_old_user(struct sysctl_req *req, const void *p,
size_t l)
return (error);
if (i < l)
return (ENOMEM);
- req->oldidx += l;
return (0);
}
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