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stateless-connect: send response end packet

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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

13
fetch-pack.c
View File

@ -1451,6 +1451,13 @@ enum fetch_state {
FETCH_DONE,
};
static void do_check_stateless_delimiter(const struct fetch_pack_args *args,
struct packet_reader *reader)
{
check_stateless_delimiter(args->stateless_rpc, reader,
_("git fetch-pack: expected response end packet"));
}
static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
int fd[2],
const struct ref *orig_ref,
@ -1535,6 +1542,10 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
/* Process ACKs/NAKs */
switch (process_acks(negotiator, &reader, &common)) {
case READY:
/*
* Don't check for response delimiter; get_pack() will
* read the rest of this response.
*/
state = FETCH_GET_PACK;
break;
case COMMON_FOUND:
@ -1542,6 +1553,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
seen_ack = 1;
/* fallthrough */
case NO_COMMON_FOUND:
do_check_stateless_delimiter(args, &reader);
state = FETCH_SEND_REQUEST;
break;
}
@ -1561,6 +1573,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
process_section_header(&reader, "packfile", 0);
if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
die(_("git fetch-pack: fetch failed."));
do_check_stateless_delimiter(args, &reader);
state = FETCH_DONE;
break;