From: Luis Chamberlain <mcgrof@kernel.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk,
gregkh@linuxfoundation.org, rostedt@goodmis.org,
mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com,
nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com,
yukuai3@huawei.com, martin.petersen@oracle.com,
jejb@linux.ibm.com, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 8/8] block: create the request_queue debugfs_dir on registration
Date: Mon, 22 Jun 2020 12:42:08 +0000 [thread overview]
Message-ID: <20200622124208.GW11244@42.do-not-panic.com> (raw)
In-Reply-To: <02112994-4cd7-c749-6bd7-66a772593c90@acm.org>
On Sat, Jun 20, 2020 at 11:07:43AM -0700, Bart Van Assche wrote:
> On 2020-06-19 13:47, Luis Chamberlain wrote:
> > We were only creating the request_queue debugfs_dir only
> > for make_request block drivers (multiqueue), but never for
> > request-based block drivers. We did this as we were only
> > creating non-blktrace additional debugfs files on that directory
> > for make_request drivers. However, since blktrace *always* creates
> > that directory anyway, we special-case the use of that directory
> > on blktrace. Other than this being an eye-sore, this exposes
> > request-based block drivers to the same debugfs fragile
> > race that used to exist with make_request block drivers
> > where if we start adding files onto that directory we can later
> > run a race with a double removal of dentries on the directory
> > if we don't deal with this carefully on blktrace.
> >
> > Instead, just simplify things by always creating the request_queue
> > debugfs_dir on request_queue registration. Rename the mutex also to
> > reflect the fact that this is used outside of the blktrace context.
>
> There are two changes in this patch: a bug fix and a rename of a mutex.
> I don't like it to see two changes in a single patch.
I thought about doing the split first, and I did it at first, but
then I could hear Christoph yelling at me for it. So I merged the
two together. Although it makes it more difficult for review,
the changes do go together.
Kind of late to split this as its already merged now.
> Additionally, is the new mutex name really better than the old name? The
> proper way to use mutexes is to use mutexes to protect data instead of
> code. Where is the documentation that mentions which member variable(s)
> of which data structures are protected by the mutex formerly called
> blk_trace_mutex?
It does not exist, and that is the point. The debugfs_dir use after
free showed us *when* that UAF can happen, and so care must be taken
if we are to use the mutex to protect the debugfs_dir but also re-use
the same directory for other block core shenanigans.
> Since the new name makes it even less clear which data
> is protected by this mutex, is the new name really better than the old name?
I thought the new name makes it crystal clear what is being protected. I
can however add a comment to explain that the q->debugfs_mutex protects
the q->debugfs_dir if it is created, otherwise it protects the ephemeral
debugfs_dir directory which would otherwise be created in lieue of
q->debugfs_dir, however the patch still lies under <debugfs_root>/block/.
Let me know if you think that will help.
Luis
next prev parent reply other threads:[~2020-06-22 12:42 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 20:47 [PATCH v7 0/8] blktrace: fix debugfs use after free Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 1/8] block: add docs for gendisk / request_queue refcount helpers Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 2/8] block: clarify context for refcount increment helpers Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 3/8] block: revert back to synchronous request_queue removal Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 4/8] blktrace: annotate required lock on do_blk_trace_setup() Luis Chamberlain
2020-06-20 17:02 ` Bart Van Assche
2020-06-19 20:47 ` [PATCH v7 5/8] loop: be paranoid on exit and prevent new additions / removals Luis Chamberlain
2020-06-20 17:11 ` Bart Van Assche
2020-06-22 12:27 ` Luis Chamberlain
2020-06-23 2:16 ` Bart Van Assche
2020-06-23 16:56 ` Luis Chamberlain
2020-06-23 17:05 ` Johannes Thumshirn
2020-06-24 12:08 ` Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 6/8] blktrace: fix debugfs use after free Luis Chamberlain
2020-06-20 7:29 ` Christoph Hellwig
2020-06-20 17:31 ` Bart Van Assche
2020-06-22 12:36 ` Luis Chamberlain
2020-06-19 20:47 ` [PATCH v7 7/8] blktrace: ensure our debugfs dir exists Luis Chamberlain
2020-06-20 7:29 ` Christoph Hellwig
2020-06-20 17:33 ` Bart Van Assche
2020-06-19 20:47 ` [PATCH v7 8/8] block: create the request_queue debugfs_dir on registration Luis Chamberlain
2020-06-20 7:30 ` Christoph Hellwig
2020-06-20 18:07 ` Bart Van Assche
2020-06-22 12:42 ` Luis Chamberlain [this message]
2020-06-23 3:18 ` Bart Van Assche
2020-06-20 21:18 ` [PATCH v7 0/8] blktrace: fix debugfs use after free Jens Axboe
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