Re: [PATCH] imap-send: increase command size limit

From: Jeff King <peff@peff.net>
Date: Apr 17, 2024, 00:24 UTC
Message-ID: <20240417002454.GA2305596@coredump.intra.peff.net>
In-Reply-To: <85047e64-044f-4bf8-8de9-33b082255f3e@web.de>

On Tue, Apr 16, 2024 at 06:08:05PM +0200, René Scharfe wrote:

> > Shouldn't socket_write() just use size_t / ssize_t?
> 
> Probably size_t.

Yes, but you need ssize_t to handle the negative return values.

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> > In particular, this made me wonder what we would do for larger items.
> > Like, say, the actual message to be uploaded. And indeed, we use a
> > strbuf to read in the messages and pass the whole buffer for each to
> > socket_write(). So we'd possibly quietly truncate such a message.
> 
> Hmm, perhaps we should at least sprinkle in some more overflow checks?

Perhaps, but...

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> > Fixing it is a little more complicated than switching to size_t, because
> > the underlying SSL_write() uses an int. So we'd probably need some
> > looping, similar to xwrite().
> 
> Or SSL_write_ex(), which takes and returns size_t.  It was added in
> OpenSSL 1.1.1, which reached its end of life half a year ago.
> 
> https://www.openssl.org/docs/man1.1.1/man3/SSL_write.html
> https://www.openssl.org/blog/blog/2023/03/28/1.1.1-EOL/

You'd think that when I ran "man SSL_write" while writing the other email I would have noticed that SSL_write_ex() is mentioned right there in the synopsis. But somehow I didn't.

I don't think we document a required version for ssl. That version is "only" 5.5 years old, but I think it would be OK here (especially given that imap-send is an optional component with a build-time knob).

In which case I think fixing socket_write() would fix this problem, and then building your other patch on top, it doesn't need to worry about INT_MAX at all.

Looking at the conversion, I think there's a slight gotcha with retaining the "0" return value from SSL_write_ex() to pass to socket_perror() in the error path. Which makes me wonder about that error path at all; it closes descriptors but doesn't handle SSL at all. Should it be using socket_shutdown()? And should that function set sock->ssl to NULL and the descriptors to -1? The rabbit hole of imap-send is infinite.

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> > In practice I doubt this is ever an issue. 2GB emails are not likely to
> > be usable in general.
> 
> Tough.  Who likes to get multi-GB patches in their inbox?  Heard of
> people exchanging CD images by email decades ago, though, so I
> wouldn't rule this out totally.  Perhaps that's the last puzzle piece
> to convert game studios to perform email reviews of asset-heavy
> binary diffs? ;-)

OK, I laughed out loud at this. Perhaps a sign of too much Git.

-Peff