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Date:   Fri, 24 Feb 2017 15:35:23 -0500
From:   Jeff King <peff@peff.net>
To:     Junio C Hamano <gitster@pobox.com>
Cc:     Johannes Schindelin <johannes.schindelin@gmx.de>,
        git@vger.kernel.org,
        Christophe Macabiau <christophemacabiau@gmail.com>
Subject: Re: fatal error when diffing changed symlinks
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On Fri, Feb 24, 2017 at 11:51:22AM -0800, Junio C Hamano wrote:

> > A slightly worse is that the upcoming Git will ship with a rewritten
> > "difftool" that makes the above sequence segfault.
> 
> The culprit seems to be these lines in run_dir_diff():
> 
> 		if (S_ISLNK(lmode)) {
> 			char *content = read_sha1_file(loid.hash, &type, &size);
> 			add_left_or_right(&symlinks2, src_path, content, 0);
> 			free(content);
> 		}
> 
> 		if (S_ISLNK(rmode)) {
> 			char *content = read_sha1_file(roid.hash, &type, &size);
> 			add_left_or_right(&symlinks2, dst_path, content, 1);
> 			free(content);
> 		}
> 
> When viewing a working tree file, oid.hash could be 0{40} and
> read_sha1_file() is not the right function to use to obtain the
> contents.
> 
> Both of these two need to pay attention to 0{40}, I think, as the
> user may be running "difftool -R --dir-diff" in which case the
> working tree would appear in the left hand side instead.

As a side note, I think even outside of 0{40}, this should be checking
the return value of read_sha1_file(). A corrupted repo should die(), not
segfault.

-Peff