Re: [PATCH] do not read beyond end of malloc'd buffer

Junio C Hamano wrote:

Jim Meyering [off-list ref] writes:

quoted

I was surprised to see "git diff --word-diff" output a ton of
garbage, and tracked it down to a bug that's triggered when the
diff.suppress-blank-empty config option to true and when at least
one of the context lines is empty.

Heh, I am not that surprised ;-)

I think the real culprit is a year-old 882749a (diff: add --word-diff
option that generalizes --color-words, 2010-04-14); it probably shows that
not many people use diff.s-b-e settings?

That must be the issue: too few people know to use diff.s-b-e.
If a few more of us were to set that option by running this command:

    git config --global diff.suppress-blank-empty true

(to suppress emission of trailing blanks on empty context lines)
then bugs like this would be exposed more quickly.

...

It is a bit unfortunate that we cannot make this into a test script, as it
depends on what is on the uninitialized part of the heap, which might
happen to be a NUL in which case the test would pass.

Running tests under the valgrind mode may catch issues, though.

Right, since reading the trailing NUL byte after the
end of the buffer would be detected.

Thanks. Will queue with this test squashed in.

Thanks for adding the test!