unblock and unignore SIGPIPE

Blocked and ignored signals -- but not caught signals -- are inherited
across exec.  Some callers with sloppy signal-handling behavior can call
git with SIGPIPE blocked or ignored, even non-deterministically.  When
SIGPIPE is blocked or ignored, several git commands can run indefinitely,
ignoring EPIPE returns from write() calls, even when the process that
called them has gone away.  Our specific case involved a pipe of git
diff-tree output to a script that reads a limited amount of diff data.

In an ideal world, git would never be called with SIGPIPE blocked or
ignored.  But in the real world, several real potential callers, including
Perl, Apache, and Unicorn, sometimes spawn subprocesses with SIGPIPE
ignored.  It is easier and more productive to harden git against this
mistake than to clean it up in every potential parent process.

Signed-off-by: Patrick Reynolds <patrick.reynolds@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/t/t0005-signals.sh b/t/t0005-signals.sh
index 981437b3a8..638a355906 100755
--- a/t/t0005-signals.sh
+++ b/t/t0005-signals.sh
@@ -27,4 +27,26 @@ test_expect_success !MINGW 'signals are propagated using shell convention' '
 	test_expect_code 143 git sigterm
 '
 
+large_git () {
+	for i in $(test_seq 1 100)
+	do
+		git diff --cached --binary || return
+	done
+}
+
+test_expect_success 'create blob' '
+	test-genrandom foo 16384 >file &&
+	git add file
+'
+
+test_expect_success 'a constipated git dies with SIGPIPE' '
+	OUT=$( ((large_git; echo $? 1>&3) | :) 3>&1 )
+	test "$OUT" -eq 141
+'
+
+test_expect_success 'a constipated git dies with SIGPIPE even if parent ignores it' '
+	OUT=$( ((trap "" PIPE; large_git; echo $? 1>&3) | :) 3>&1 )
+	test "$OUT" -eq 141
+'
+
 test_done