[PATCH 1/1] upload-pack: fix race condition in error messages

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: Aug 28, 2019, 01:43 UTC
Message-ID: <5c313aba7e97cb93e7d07f6d5dfaf0febe8a2f8b.1566956608.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.324.git.gitgitgadget@gmail.com>

From: Derrick Stolee <dstolee@microsoft.com>

Test t5516-fetch-push.sh has a test 'deny fetch unreachable SHA1, allowtipsha1inwant=true' that checks stderr for a specific error string from the remote. In some build environments the error sent over the remote connection gets mingled with the error from the die() statement. Since both signals are being output to the same file descriptor (but from parent and child processes), the output we are matching with grep gets split.

To reduce the risk of this failure, follow this process instead:

1. Write an error message to stderr.
2. Write an error message across the connection.
3. exit(1).

This reorders the events so the error is written entirely before the client receives a message from the remote, removing the race condition.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 upload-pack.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/upload-pack.c b/upload-pack.c
index 222cd3ad89..b0d3e028d1 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -613,11 +613,12 @@ static void check_non_tip(struct object_array *want_obj,
 	for (i = 0; i < want_obj->nr; i++) {
 		struct object *o = want_obj->objects[i].item;
 		if (!is_our_ref(o)) {
+			warning("git upload-pack: not our ref %s",
+				oid_to_hex(&o->oid));
 			packet_writer_error(writer,
 					    "upload-pack: not our ref %s",
 					    oid_to_hex(&o->oid));
-			die("git upload-pack: not our ref %s",
-			    oid_to_hex(&o->oid));
+			exit(1);
 		}
 	}
 }

-- 
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