mirrors/git
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

stateless-connect: send response end packet

Browse Source 
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>
This commit is contained in:
Denton Liu
2020-05-19 06:54:00 -04:00
committed by Junio C Hamano
parent 0181b600a6
commit b0df0c16ea
10 changed files with 60 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
remote-curl.c
View File

@ -703,6 +703,8 @@ static void check_pktline(struct check_pktline_state *state, const char *ptr, si
state->remaining = packet_length(state->len_buf);
if (state->remaining < 0) {
die(_("remote-curl: bad line length character: %.4s"), state->len_buf);
} else if (state->remaining == 2) {
die(_("remote-curl: unexpected response end packet"));
} else if (state->remaining < 4) {
state->remaining = 0;
} else {
@ -991,6 +993,9 @@ retry:
if (rpc_in_data.pktline_state.remaining)
err = error(_("%d bytes of body are still expected"), rpc_in_data.pktline_state.remaining);
if (stateless_connect)
packet_response_end(rpc->in);
curl_slist_free_all(headers);
free(gzip_body);
return err;