From: Mike Snitzer <snitzer@redhat.com>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Alasdair G Kergon <agk@redhat.com>,
"dm-devel@redhat.com" <dm-devel@redhat.com>,
"keescook@chromium.org" <keescook@chromium.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"shli@kernel.org" <shli@kernel.org>,
"koverstreet@google.com" <koverstreet@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
"linux-bcache@vger.kernel.org" <linux-bcache@vger.kernel.org>,
"ejt@redhat.com" <ejt@redhat.com>,
"kent.overstreet@gmail.com" <kent.overstreet@gmail.com>,
Zdenek Kabelac <zkabelac@redhat.com>
Subject: Re: [PATCH 3/4] dm: convert dm_dev_internal.count from atomic_t to refcount_t
Date: Tue, 28 Nov 2017 14:02:43 -0500 [thread overview]
Message-ID: <20171128190225.GA32559@redhat.com> (raw)
In-Reply-To: <2236FBA76BA1254E88B949DDB74E612B802C3EDA@IRSMSX102.ger.corp.intel.com>
On Tue, Nov 28 2017 at 5:07am -0500,
Reshetova, Elena <elena.reshetova@intel.com> wrote:
>
> > On Fri, Nov 24, 2017 at 2:36 AM, Reshetova, Elena
> > <elena.reshetova@intel.com> wrote:
> > >> On Fri, Oct 20, 2017 at 10:37:38AM +0300, Elena Reshetova wrote:
> > >> > } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
> > >> > r = upgrade_mode(dd, mode, t->md);
> > >> > if (r)
> > >> > return r;
> > >> > + refcount_inc(&dd->count);
> > >> > }
> > >>
> > >> Missing here:
> > >>
> > >> else
> > >> refcount_inc(&dd->count);
> > >>
> > >> ?
> > >
> > > Oh, yes, thanks for catching this! I think this got unnoticed so far and patch was
> > merged, so I am going to send a followup patch now.
> >
> > I pushed this fix and will send to Linus next week:
> > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-
> > dm.git/commit/?h=dm-4.15&id=d908af82d06cc420f9581c97c6db941cb87e4434
>
>
> I guess you mean this commit:
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=c2318d07ead871f058dda62e942ed7b6b1c1cfcf
>
> Unfortunately it is not correct:
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 88130b5..f6d32ee 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -451,15 +451,15 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> return r;
> }
>
> - refcount_set(&dd->count, 1);
> + refcount_set(&dd->count, 0);
> list_add(&dd->list, &t->devices);
>
> } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
> r = upgrade_mode(dd, mode, t->md);
> if (r)
> return r;
> - refcount_inc(&dd->count);
> }
> + refcount_inc(&dd->count);
>
> Problem will be here if you hit this refcount_inc() after the refcount_set(&dd->count, 0) earlier.
> refcount_inc() does not increment on zero value *ever* for security reasons and instead people
> should initialize refcounters to 1 always and do increments from there if needed.
include/linux/refcount.h:refcount_inc() definitely doesn't avoid
incrementing zero value.
Neither does lib/refcount.c:refcount_inc() but it does spew a WARN_ON by
assuming a zero value means use-after-free.
> This was the reason for the initial change I did, my mistake was just to forget to increment it also
> in case condition (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) fails.
>
> I have issues with my intel smpt server for sending patches (I will get it fixed tomorrow from internal network),
> so I am attaching the patch I did end of last week to this thread instead (or alternatively can properly send it tomorrow after fix).
> Sorry for the delay!
I was tempted to revert your original commits that switch DM code to
using refcount_t. Already proved more trouble than it is worth.
But I'll drop my commit and take your fix.
Mike
next prev parent reply other threads:[~2017-11-28 19:02 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-20 7:37 [PATCH 0/4] dm and bcache refcount conversions Elena Reshetova
2017-10-20 7:37 ` [PATCH 1/4] bcache: convert cached_dev.count from atomic_t to refcount_t Elena Reshetova
2017-10-20 18:39 ` Michael Lyle
2017-10-23 6:45 ` Reshetova, Elena
2017-10-20 7:37 ` [PATCH 2/4] dm cache: convert dm_cache_metadata.ref_count " Elena Reshetova
2017-10-20 7:37 ` [PATCH 3/4] dm: convert dm_dev_internal.count " Elena Reshetova
2017-11-23 15:49 ` [dm-devel] " Alasdair G Kergon
2017-11-24 7:36 ` Reshetova, Elena
2017-11-25 5:56 ` Mike Snitzer
2017-11-28 10:07 ` Reshetova, Elena
2017-11-28 19:02 ` Mike Snitzer [this message]
2017-11-29 8:05 ` Reshetova, Elena
2017-10-20 7:37 ` [PATCH 4/4] dm: convert table_device.count " Elena Reshetova
2017-11-23 15:19 ` Zdenek Kabelac
2017-11-24 8:29 ` Reshetova, Elena
2017-11-24 14:04 ` Alasdair G Kergon
2017-11-24 14:44 ` Reshetova, Elena
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