linux-ext4 - Re: [PATCH v5] e2fsck: check for consistent encryption policies

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Date:   Wed, 18 Sep 2019 17:06:43 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-ext4@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v5] e2fsck: check for consistent encryption policies

On Sep 17, 2019, at 7:07 PM, Eric Biggers <ebiggers@...nel.org> wrote:
> 
> From: Eric Biggers <ebiggers@...gle.com>
> 
> By design, the kernel enforces that all files in an encrypted directory
> use the same encryption policy as the directory.  It's not possible to
> violate this constraint using syscalls.  Lookups of files that violate
> this constraint also fail, in case the disk was manipulated.
> 
> But this constraint can also be violated by accidental filesystem
> corruption.  E.g., a power cut when using ext4 without a journal might
> leave new files without the encryption bit and/or xattr.  Thus, it's
> important that e2fsck correct this condition.
> 
> Therefore, this patch makes the following changes to e2fsck:
> 
> - During pass 1 (inode table scan), create a map from inode number to
>  encryption policy for all encrypted inodes.  But it's optimized so
>  that the full xattrs aren't saved but rather only 32-bit "policy IDs",
>  since usually many inodes share the same encryption policy.  Also, if
>  an encryption xattr is missing, offer to clear the encrypt flag.  If
>  an encryption xattr is clearly corrupt, offer to clear the inode.
> 
> - During pass 2 (directory structure check), use the map to verify that
>  all regular files, directories, and symlinks in encrypted directories
>  use the directory's encryption policy.  Offer to clear any directory
>  entries for which this isn't the case.
> 
> Add a new test "f_bad_encryption" to test the new behavior.
> 
> Due to the new checks, it was also necessary to update the existing test
> "f_short_encrypted_dirent" to add an encryption xattr to the test file,
> since it was missing one before, which is now considered invalid.
> 
> Google-Bug-Id: 135138675
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>


Cheers, Andreas






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