linux-ext4 - Re: [PATCH] ext4: fix fallocate to use file_modified to update permissions consistently

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Date:   Wed, 9 Mar 2022 20:31:09 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Theodore Ts'o <tytso@....edu>,
        linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: fix fallocate to use file_modified to update
 permissions consistently

On Tue, Mar 08, 2022 at 10:50:43AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@...nel.org>
> 
> Since the initial introduction of (posix) fallocate back at the turn of
> the century, it has been possible to use this syscall to change the
> user-visible contents of files.  This can happen by extending the file
> size during a preallocation, or through any of the newer modes (punch,
> zero, collapse, insert range).  Because the call can be used to change
> file contents, we should treat it like we do any other modification to a
> file -- update the mtime, and drop set[ug]id privileges/capabilities.
> 
> The VFS function file_modified() does all this for us if pass it a
> locked inode, so let's make fallocate drop permissions correctly.
> 
> Signed-off-by: Darrick J. Wong <djwong@...nel.org>
> ---
>  fs/ext4/ext4.h    |    2 +-
>  fs/ext4/extents.c |   32 +++++++++++++++++++++++++-------
>  fs/ext4/inode.c   |    7 ++++++-
>  3 files changed, 32 insertions(+), 9 deletions(-)

Is there a test in xfstests that tests for this?

- Eric