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From: Al Viro <viro@zeniv.linux.org.uk>
To: Daniel Rosenberg <drosen@google.com>
Cc: kernel-team@android.com, Theodore Ts'o <tytso@mit.edu>,
	Jonathan Corbet <corbet@lwn.net>,
	Richard Weinberger <richard@nod.at>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	Eric Biggers <ebiggers@kernel.org>,
	linux-fscrypt@vger.kernel.org, linux-mtd@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-ext4@vger.kernel.org,
	Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [f2fs-dev] [PATCH v7 2/8] fs: Add standard casefolding support
Date: Mon, 10 Feb 2020 23:42:07 +0000
Message-ID: <20200210234207.GJ23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CA+PiJmTYbEA-hgrKwtp0jZXqsfYrzgogOZ0Pt=gTCtqhBfnqFA@mail.gmail.com>

On Mon, Feb 10, 2020 at 03:11:13PM -0800, Daniel Rosenberg wrote:
> On Fri, Feb 7, 2020 at 6:12 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Fri, Feb 07, 2020 at 05:35:46PM -0800, Daniel Rosenberg wrote:
> >
> >
> > Again, is that safe in case when the contents of the string str points to
> > keeps changing under you?
> 
> I'm not sure what you mean. I thought it was safe to use the str and
> len passed into d_compare. Even if it gets changed under RCU
> conditions I thought there was some code to ensure that the name/len
> pair passed in is consistent, and any other inconsistencies would get
> caught by d_seq later. Are there unsafe code paths that can follow?

If you ever fetch the same byte twice, you might see different values.
You need a fairly careful use of READ_ONCE() or equivalents to make
sure that you don't get screwed over by that.

Sure, ->d_seq mismatch will throw the result out, but you need to make
sure you won't oops/step on uninitialized memory/etc. in process.

It's not impossible to get right, but it's not trivial and you need all
code working with that much more careful than normal for string handling.


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Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-08  1:35 [f2fs-dev] [PATCH v7 0/8] Support fof Casefolding and Encryption Daniel Rosenberg via Linux-f2fs-devel
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 1/8] unicode: Add utf8_casefold_iter Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  3:38   ` Eric Biggers
2020-02-14 21:47     ` Daniel Rosenberg via Linux-f2fs-devel
2020-02-17 19:02       ` Gabriel Krisman Bertazi
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 2/8] fs: Add standard casefolding support Daniel Rosenberg via Linux-f2fs-devel
2020-02-08  2:12   ` Al Viro
2020-02-10 23:11     ` Daniel Rosenberg via Linux-f2fs-devel
2020-02-10 23:42       ` Al Viro [this message]
2020-02-12  6:34         ` Eric Biggers
2020-02-12  6:57           ` Eric Biggers
2020-02-20  2:27             ` Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  3:55   ` Eric Biggers
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 3/8] f2fs: Use generic " Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  4:05   ` Eric Biggers
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 4/8] ext4: " Daniel Rosenberg via Linux-f2fs-devel
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 5/8] fscrypt: Have filesystems handle their d_ops Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  4:33   ` Eric Biggers
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 6/8] f2fs: Handle casefolding with Encryption Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  5:10   ` Eric Biggers
2020-02-12  5:55     ` Al Viro
2020-02-12  6:06       ` Eric Biggers
2020-02-12  5:47   ` Eric Biggers
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 7/8] ext4: Hande casefolding with encryption Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  5:59   ` Eric Biggers
2020-02-08  1:35 ` [f2fs-dev] [PATCH v7 8/8] ext4: Optimize match for casefolded encrypted dirs Daniel Rosenberg via Linux-f2fs-devel
2020-02-12  6:12 ` [f2fs-dev] [PATCH v7 0/8] Support fof Casefolding and Encryption Eric Biggers
2020-02-13  0:01   ` Daniel Rosenberg via Linux-f2fs-devel

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