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authorDenton Liu <liu.denton@gmail.com>2020-05-19 10:54:00 (GMT)
committerJunio C Hamano <gitster@pobox.com>2020-05-24 23:26:00 (GMT)
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stateless-connect: send response end packet
Currently, remote-curl acts as a proxy and blindly forwards packets between an HTTP server and fetch-pack. In the case of a stateless RPC connection where the connection is terminated before the transaction is complete, remote-curl will blindly forward the packets before waiting on more input from fetch-pack. Meanwhile, fetch-pack will read the transaction and continue reading, expecting more input to continue the transaction. This results in a deadlock between the two processes. This can be seen in the following command which does not terminate: $ git -c protocol.version=2 clone https://github.com/git/git.git --shallow-since=20151012 Cloning into 'git'... whereas the v1 version does terminate as expected: $ git -c protocol.version=1 clone https://github.com/git/git.git --shallow-since=20151012 Cloning into 'git'... fatal: the remote end hung up unexpectedly Instead of blindly forwarding packets, make remote-curl insert a response end packet after proxying the responses from the remote server when using stateless_connect(). On the RPC client side, ensure that each response ends as described. A separate control packet is chosen because we need to be able to differentiate between what the remote server sends and remote-curl's control packets. By ensuring in the remote-curl code that a server cannot send response end packets, we prevent a malicious server from being able to perform a denial of service attack in which they spoof a response end packet and cause the described deadlock to happen. Reported-by: Force Charlie <charlieio@outlook.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Denton Liu <liu.denton@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 files changed, 3 insertions, 1 deletions
diff --git a/Documentation/gitremote-helpers.txt b/Documentation/gitremote-helpers.txt
index f48a031..93baeeb 100644
--- a/Documentation/gitremote-helpers.txt
+++ b/Documentation/gitremote-helpers.txt
@@ -405,7 +405,9 @@ Supported if the helper has the "connect" capability.
trying to fall back). After line feed terminating the positive
(empty) response, the output of the service starts. Messages
(both request and response) must consist of zero or more
- PKT-LINEs, terminating in a flush packet. The client must not
+ PKT-LINEs, terminating in a flush packet. Response messages will
+ then have a response end packet after the flush packet to
+ indicate the end of a response. The client must not
expect the server to store any state in between request-response
pairs. After the connection ends, the remote helper exits.
+