linux-ext4 - Re: [PATCH v4 00/16] fs-verity: read-only file-based authenticity protection

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Message-ID: <CAHk-=wgSzRzoro8ATO5xb6OFxN1A0fjUCQSAHfGuEPbEu+zWvA@mail.gmail.com>
Date:   Thu, 6 Jun 2019 10:21:12 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-integrity@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>
Subject: Re: [PATCH v4 00/16] fs-verity: read-only file-based authenticity protection

On Thu, Jun 6, 2019 at 8:54 AM Eric Biggers <ebiggers@...nel.org> wrote:
>
> This is a redesigned version of the fs-verity patchset, implementing
> Ted's suggestion to build the Merkle tree in the kernel
> (https://lore.kernel.org/linux-fsdevel/20190207031101.GA7387@mit.edu/).
> This greatly simplifies the UAPI, since the verity metadata no longer
> needs to be transferred to the kernel.

Interfaces look sane to me. My only real concern is whether it would
make sense to make the FS_IOC_ENABLE_VERITY ioctl be something that
could be done incrementally, since the way it is done now it looks
like any random user could create a big file and then do the
FS_IOC_ENABLE_VERITY to make the kernel do a _very_ expensive
operation.

Yes, I see the

+               if (fatal_signal_pending(current))
+                       return -EINTR;
+               cond_resched();

in there, so it's not like it's some entirely unkillable thing, and
maybe we don't care as a result. But maybe the ioctl interface could
be fundamentally restartable?

If that was already considered and people just went "too complex", never mind.

               Linus