[PATCH 1/6] receive-pack: fix deadlock when we cannot create tmpdir

[Jeff King <peff@peff.net>]

The err_fd descriptor passed to the unpack() function is
intended to be handed off to the child index-pack, and our
async muxer will read until it gets EOF. However, if we
encounter an error before handing off the descriptor, we
must manually close(err_fd). Otherwise we will be waiting
for our muxer to finish, while the muxer is waiting for EOF
on err_fd.

We fixed an identical deadlock already in 49ecfa13f
(receive-pack: close sideband fd on early pack errors,
2013-04-19). But since then, the function grew a new
early-return in 722ff7f87 (receive-pack: quarantine objects
until pre-receive accepts, 2016-10-03), when we fail to
create a temporary directory. This return needs the same
treatment.

Reported-by: Horst Schirmeier <horst@schirmeier.com>
Signed-off-by: Jeff King <peff@peff.net>
---
 builtin/receive-pack.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 9ed8fbbfa..f2c6953a3 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1667,8 +1667,11 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 	}
 
 	tmp_objdir = tmp_objdir_create();
-	if (!tmp_objdir)
+	if (!tmp_objdir) {
+		if (err_fd > 0)
+			close(err_fd);
 		return "unable to create temporary object directory";
+	}
 	child.env = tmp_objdir_env(tmp_objdir);
 
 	/*
-- 
2.12.0.429.gde83c8049