linux-ext4 - Re: [PATCH v5 01/10] fs: Expose helper to check if a directory needs casefolding

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Message-ID: <20230813043022.GA3545@sol.localdomain>
Date:   Sat, 12 Aug 2023 21:30:22 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Theodore Ts'o <tytso@....edu>,
        Gabriel Krisman Bertazi <krisman@...e.de>,
        viro@...iv.linux.org.uk, brauner@...nel.org, jaegeuk@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH v5 01/10] fs: Expose helper to check if a directory needs
 casefolding

On Sun, Aug 13, 2023 at 04:08:58AM +0100, Matthew Wilcox wrote:
> On Sat, Aug 12, 2023 at 07:06:47PM -0400, Theodore Ts'o wrote:
> > One could say that this is an insane threat model, but the syzbot team
> > thinks that this can be used to break out of a kernel lockdown after a
> > UEFI secure boot.  Which is fine, except I don't think I've been able
> > to get any company (including Google) to pay for headcount to fix
> > problems like this, and the unremitting stream of these sorts of
> > syzbot reports have already caused one major file system developer to
> > burn out and step down.
> > 
> > So problems like this get fixed on my own time, and when I have some
> > free time.  And if we "simplify" the code, it will inevitably cause
> > more syzbot reports, which I will then have to ignore, and the syzbot
> > team will write more "kernel security disaster" slide deck
> > presentations to senior VP's, although I'll note this has never
> > resulted in my getting any additional SWE's to help me fix the
> > problem...
> > 
> > > So just __ext4_iget() needs to be fixed.  I think we should consider doing that
> > > before further entrenching all the extra ->s_encoding checks.
> > 
> > If we can get an upstream kernel consensus that syzbot reports caused
> > by writing to a mounted file system aren't important, and we can
> > publish this somewhere where hopefully the syzbot team will pay
> > attention to it, sure...
> 
> What the syzbot team don't seem to understand is that more bug reports
> aren't better.  I used to investigate one most days, but the onslaught is
> relentless and I just ignore syzbot reports now.  I appreciate maintainers
> don't necessarily get that privilege.
> 
> They seem motivated to find new and exciting ways to break the kernel
> without realising that they're sapping the will to work on the bugs that
> we already have.
> 

Well, one thing that the kernel community can do to make things better is
identify when a large number of bug reports are caused by a single issue
("userspace can write to mounted block devices"), and do something about that
underlying issue (https://lore.kernel.org/r/20230704122727.17096-1-jack@suse.cz)
instead of trying to "fix" large numbers of individual "bugs".  We can have 1000
bugs or 1 bug, it is actually our choice in this case.

- Eric