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

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Message-ID: <YjyGToTy8cHtytun@mit.edu>
Date:   Thu, 24 Mar 2022 10:55:10 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     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>

Applied, thanks!

(BTW, when you reply to a patch with a different patch, such as in
this case, "fstests: ensure we drop suid after fallocate", it
hopelessly confuses b4, which is why I'm sending this notification
manually.  Try running "b4 am 20220308185043.GA117678@...nolia" and
compare that to https://lore.kernel.org/r/20220308185043.GA117678@magnolia
and you'll see what I mean.)

					- Ted