linux-ext4 - Re: [PATCH v3 02/10] fscrypt: Share code between functions that prepare lookup

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Date: Thu, 25 Jan 2024 17:18:00 -0300
From: Gabriel Krisman Bertazi <krisman@...e.de>
To: Eric Biggers <ebiggers@...nel.org>
Cc: viro@...iv.linux.org.uk,  jaegeuk@...nel.org,  tytso@....edu,
  linux-ext4@...r.kernel.org,  linux-f2fs-devel@...ts.sourceforge.net,
  linux-fsdevel@...r.kernel.org,  amir73il@...il.com
Subject: Re: [PATCH v3 02/10] fscrypt: Share code between functions that
 prepare lookup

Eric Biggers <ebiggers@...nel.org> writes:

> On Fri, Jan 19, 2024 at 03:47:34PM -0300, Gabriel Krisman Bertazi wrote:
>> To make the patch simpler, we now call fscrypt_get_encryption_info twice
>> for fscrypt_prepare_lookup, once inside fscrypt_setup_filename and once
>> inside fscrypt_prepare_lookup_dentry.  It seems safe to do, and
>> considering it will bail early in the second lookup and most lookups
>> should go to the dcache anyway, it doesn't seem problematic for
>> performance.  In addition, we add a function call for the unencrypted
>> case, also during lookup.
>
> Unfortunately I don't think it's correct.  This is basically undoing my fix
> b01531db6cec ("fscrypt: fix race where ->lookup() marks plaintext dentry as
> ciphertext") from several years ago.
>
> When a lookup is done, the filesystem needs to either treat the name being
> looked up as a no-key name *or* as a regular name, depending on whether the
> directory's key is present.  We shouldn't enable race conditions where, due to
> the key being concurrently added, the name is treated as a no-key name for
> filename matching purposes but a regular name for dentry validation purposes.
> That can result in an anomaly where a file that exists ends up with a negative
> dentry that doesn't get invalidated.
>
> Basically, the boolean fscrypt_name::is_nokey_name that's produced by
> fscrypt_setup_filename() should continue to be propagated to DCACHE_NOKEY_NAME.

I see your point.  I'll drop this patch and replace it with a patch that
just merges the DCACHE_NOKEY_NAME configuration.  Sadly, we gotta keep
the two variants I think.

thanks for the review

-- 
Gabriel Krisman Bertazi