Re: [PATCH v3 2/3] commit-graph: fix buffer read-overflow

From: Jeff King <peff@peff.net>
Date: Dec 11, 2018, 09:50 UTC
Message-ID: <20181211095002.GB31588@sigill.intra.peff.net>
In-Reply-To: <20181210215649.GC37614@google.com>

On Mon, Dec 10, 2018 at 01:56:49PM -0800, Josh Steadmon wrote:

Show 9 quoted lines

> > "stat(1)" is not so portable, so you'll get complaints from minority
> > platform users later.  So is "truncate(1)".
> 
> Ack, thanks for the catch. I have a workaround for stat in the form of
> "wc -c", and for truncate with a combination of dd and /dev/zero.
> However, I'm finding conflicting information about whether or not
> /dev/zero exists on macOS. At the least, it sounds like it might not
> work on very old versions. Would this be acceptable, or should I add a
> new test function to do this?

If you're just interested in truncation (and not a bunch of zero bytes), you can dd from /dev/null.

Another way to truncate is to move the file elsewhere, and then copy only some of the bytes back (see t1450's "fsck detects truncated loose object").

-Peff