Re: [PATCH 1/2] read_and_strip_branch: fix typo'd address-of operator

Jeff King [off-list ref] writes:

When we are chomping newlines from the end of a strbuf, we
must check "sb.len != 0" before accessing "sb.buf[sb.len - 1]".
However, this code mistakenly checks "&sb.len", which is
always true (it is a part of an auto struct, so the address
is always non-zero). This could lead to us accessing memory
outside the strbuf when we read an empty file.

Signed-off-by: Jeff King <redacted>
---
This dates back to 8b87cfd (wt-status: move strbuf into
read_and_strip_branch(), 2013-03-16), so it is not a bug that needs
addressed during the -rc period.

This is the most minimal fix, but I kind of wonder if it should just be
using strbuf_rtrim (or even strbuf_trim) in the first place.

Yeah.  Or strbuf_chomp(), which does not exist ;-)

It is tempting to apply this directly to maint and merge up
immediately, as there is no way this 1-byte change will break things
(of course that is not necessarily true for random 1-byte changes,
though).

It sometimes gets really hard to resist that temptation during the
pre-release freeze period.

On Wed, Jan 28, 2015 at 12:42:26PM -0800, Junio C Hamano wrote:

quoted

This is the most minimal fix, but I kind of wonder if it should just be
using strbuf_rtrim (or even strbuf_trim) in the first place.

Yeah.  Or strbuf_chomp(), which does not exist ;-)

This is not the first time I've seen this chomp/trim distinction come
up. However, the thing that has prevented me from writing strbuf_chomp
is that the trim is almost always a more reasonable choice.

Take this instance. We are opening and reading a whole file. Surely we
need to drop the final newline, which is not interesting. But we are not
just doing that; we are dropping _all_ trailing newlines. So "foo\n\n"
becomes "foo". But "foo\n \n" does not. That doesn't make much sense.

IOW, I would venture to say that chomping like this falls into one of
two categories:

  1. You want to clean up any extraneous cruft. Multiple lines, extra
     whitespace, etc.

  2. You want to read one line, but don't want the trailing newline.

And strbuf_getline already handles case (2).

End mini-rant. :)

It is tempting to apply this directly to maint and merge up
immediately, as there is no way this 1-byte change will break things
(of course that is not necessarily true for random 1-byte changes,
though).

It sometimes gets really hard to resist that temptation during the
pre-release freeze period.

That's part of why I did the simplest fix instead of strbuf_rtrim. To
tempt you. :)

-Peff