[PATCH v3 0/7] remote-curl: fix deadlocks when remote server disconnects
- From
Denton Liu <liu.denton@gmail.com>
- Date
- May 19, 2020, 10:53 UTC
- Message-ID
- <cover.1589885479.git.liu.denton@gmail.com>
- In-Reply-To
- <cover.1589816718.git.liu.denton@gmail.com>
The following command hangs forever:
$ git -c protocol.version=2 clone https://github.com/git/git.git --shallow-since=20151012 Cloning into 'git'...
This occurs because the --shallow-since arg is incorrect and the server dies early. However, remote-curl does not realise that the server errored out and just faithfully forwards the packets to fetch-pack before waiting on more input from fetch-pack. Meanwhile, fetch-pack keeps reading as it still expects more input. As a result, the processes deadlock. Original analysis by Peff: https://lore.kernel.org/git/20200328154936.GA1217052@coredump.intra.peff.net/
Changes since v2:
* Use if-else tower in "transport: extract common fetch_pack() call"
* Rename to `lenbuf_hex` and remove null-terminator sentence in "pkt-line: extern packet_length()"
* Fix "a a" typo in "remote-curl: error on incomplete packet"
* Don't send flush packet after response end packet
* Move stateless delimiter checks closer to where message processing happens in do_fetch_pack_v2()
Changes since v1:
* Remove fallthrough in switch in favour of just extracting the common call out of the switch in patch 3
* Add more detail in function comment and use `const char linelen[4]` in patch 4
* Implement most of Peff's suggestions[0] in patch 5
* Only operate on stateless_connect() in patch 5
* Add tests in patch 5
* Drop "remote-curl: ensure last packet is a flush" in favour of "stateless-connect: send response end packet"
[0]: https://lore.kernel.org/git/20200515213844.GD115445@coredump.intra.peff.net/
Denton Liu (7): remote-curl: fix typo remote-curl: remove label indentation transport: extract common fetch_pack() call pkt-line: extern packet_length() remote-curl: error on incomplete packet pkt-line: define PACKET_READ_RESPONSE_END stateless-connect: send response end packet
Documentation/gitremote-helpers.txt | 4 +- Documentation/technical/protocol-v2.txt | 2 + builtin/fetch-pack.c | 2 +- connect.c | 18 ++++- connect.h | 4 ++ fetch-pack.c | 13 ++++ pkt-line.c | 17 ++++- pkt-line.h | 11 +++ remote-curl.c | 70 +++++++++++++++++-- remote.h | 3 +- serve.c | 2 + t/helper/test-pkt-line.c | 4 ++ t/lib-httpd.sh | 2 + t/lib-httpd/apache.conf | 8 +++ .../incomplete-body-upload-pack-v2-http.sh | 3 + .../incomplete-length-upload-pack-v2-http.sh | 3 + t/t5702-protocol-v2.sh | 47 +++++++++++++ transport.c | 28 +++----- 18 files changed, 211 insertions(+), 30 deletions(-) create mode 100644 t/lib-httpd/incomplete-body-upload-pack-v2-http.sh create mode 100644 t/lib-httpd/incomplete-length-upload-pack-v2-http.sh
Range-diff against v2:
1: b390875f87 = 1: b390875f87 remote-curl: fix typo
2: a2b28c0b28 = 2: a2b28c0b28 remote-curl: remove label indentation
3: 3a42575bd5 < -: ---------- transport: extract common fetch_pack() call
-: ---------- > 3: c118baa5a2 transport: extract common fetch_pack() call
4: c2b9d033bb ! 4: 36885943b2 pkt-line: extern packet_length()
@@ Commit message
need to access the length header. In order to simplify this, extern
packet_length() so that the logic can be reused.
- Change the function parameter from a `const char *` to
- `const char linelen[4]`. Even though these two types behave identically
- as function parameters, use the array notation to semantically indicate
- exactly what this function is expecting as an argument.
+ Change the function parameter from `const char *linelen` to
+ `const char lenbuf_hex[4]`. Even though these two types behave
+ identically as function parameters, use the array notation to
+ semantically indicate exactly what this function is expecting as an
+ argument. Also, rename it from linelen to lenbuf_hex as the former
+ sounds like it should be an integral type which is misleading.
## pkt-line.c ##
@@ pkt-line.c: static int get_packet_data(int fd, char **src_buf, size_t *src_size,
@@ pkt-line.c: static int get_packet_data(int fd, char **src_buf, size_t *src_size,
}
-static int packet_length(const char *linelen)
-+int packet_length(const char linelen[4])
++int packet_length(const char lenbuf_hex[4])
{
- int val = hex2chr(linelen);
- return (val < 0) ? val : (val << 8) | hex2chr(linelen + 2);
+- int val = hex2chr(linelen);
+- return (val < 0) ? val : (val << 8) | hex2chr(linelen + 2);
++ int val = hex2chr(lenbuf_hex);
++ return (val < 0) ? val : (val << 8) | hex2chr(lenbuf_hex + 2);
+ }
+
+ enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
## pkt-line.h ##
@@ pkt-line.h: int write_packetized_from_buf(const char *src_in, size_t len, int fd_out);
@@ pkt-line.h: int write_packetized_from_buf(const char *src_in, size_t len, int fd
+/*
+ * Convert a four hex digit packet line length header into its numeric
-+ * representation. linelen should not be null-terminated.
++ * representation.
+ *
+ * If linelen contains non-hex characters, return -1. Otherwise, return the
+ * numeric value of the length header.
+ */
-+int packet_length(const char linelen[4]);
++int packet_length(const char lenbuf_hex[4]);
+
/*
* Read a packetized line into a buffer like the 'packet_read()' function but
5: 52ce5fdffd ! 5: 91d330620a remote-curl: error on incomplete packet
@@ Commit message
results in a deadlock between the two processes.
For a stateless connection, inspect packets before sending them and
- error out if a a packet line packet is incomplete.
+ error out if a packet line packet is incomplete.
Helped-by: Jeff King <peff@peff.net>
6: 744b078324 ! 6: ff83344e9e pkt-line: PACKET_READ_RESPONSE_END
@@ Metadata
Author: Denton Liu <liu.denton@gmail.com>
## Commit message ##
- pkt-line: PACKET_READ_RESPONSE_END
+ pkt-line: define PACKET_READ_RESPONSE_END
In a future commit, we will use PACKET_READ_RESPONSE_END to separate
messages proxied by remote-curl. To prepare for this, add the
7: 4b079bcd83 ! 7: c26e160fbc stateless-connect: send response end packet
@@ Commit message
Cloning into 'git'...
fatal: the remote end hung up unexpectedly
- Instead of blindly forwarding packets, make remote-curl insert response
- end and flush packets after proxying the responses from the remote
- server when using stateless_connect(). On the RPC client side, ensure
- that each response ends as described.
+ 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
@@ Documentation/gitremote-helpers.txt: Supported if the helper has the "connect" c
(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
-+ have a response end packet before the flush packet to indicate
-+ the end of a response. The client must not
++ 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.
+
@@ builtin/fetch-pack.c: int cmd_fetch_pack(int argc, const char **argv, const char
## connect.c ##
@@ connect.c: static int process_ref_v2(const char *line, struct ref ***list)
+ return ret;
+ }
+
++void check_stateless_delimiter(int stateless_rpc,
++ struct packet_reader *reader,
++ const char *error)
++{
++ if (!stateless_rpc)
++ return; /* not in stateless mode, no delimiter expected */
++ if (packet_reader_read(reader) != PACKET_READ_RESPONSE_END)
++ die("%s", error);
++}
++
struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
struct ref **list, int for_push,
const struct argv_array *ref_prefixes,
@@ connect.c: struct ref **get_remote_refs(int fd_out, struct packet_reader *reader
if (reader->status != PACKET_READ_FLUSH)
die(_("expected flush after ref listing"));
-+ if (stateless_rpc) {
-+ if (packet_reader_read(reader) != PACKET_READ_RESPONSE_END)
-+ die(_("expected response end packet after ref listing"));
-+ if (packet_reader_read(reader) != PACKET_READ_FLUSH)
-+ die(_("expected flush packet after response end"));
-+ }
++ check_stateless_delimiter(stateless_rpc, reader,
++ _("expected response end packet after ref listing"));
+
return list;
}
- ## fetch-pack.c ##
-@@ fetch-pack.c: static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
- struct fetch_negotiator negotiator_alloc;
- struct fetch_negotiator *negotiator;
- int seen_ack = 0;
-+ int check_http_delimiter;
+ ## connect.h ##
+@@ connect.h: int server_supports_v2(const char *c, int die_on_error);
+ int server_supports_feature(const char *c, const char *feature,
+ int die_on_error);
- if (args->no_dependents) {
- negotiator = NULL;
-@@ fetch-pack.c: static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
- }
-
- while (state != FETCH_DONE) {
-+ check_http_delimiter = 0;
++void check_stateless_delimiter(int stateless_rpc,
++ struct packet_reader *reader,
++ const char *error);
+
- switch (state) {
- case FETCH_CHECK_LOCAL:
- sort_ref_list(&ref, ref_compare_name);
+ #endif
+
+ ## fetch-pack.c ##
+@@ fetch-pack.c: 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,
@@ fetch-pack.c: 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:
+@@ fetch-pack.c: 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;
-+ check_http_delimiter = 1;
break;
}
- break;
@@ fetch-pack.c: 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;
-+ check_http_delimiter = 1;
break;
- case FETCH_DONE:
- continue;
- }
-+
-+ if (args->stateless_rpc && check_http_delimiter) {
-+ if (packet_reader_read(&reader) != PACKET_READ_RESPONSE_END)
-+ die(_("git fetch-pack: expected response end packet"));
-+ if (packet_reader_read(&reader) != PACKET_READ_FLUSH)
-+ die(_("git fetch-pack: expected flush packet"));
-+ }
- }
-
- if (negotiator)
## remote-curl.c ##
@@ remote-curl.c: static void check_pktline(struct check_pktline_state *state, const char *ptr, si
@@ remote-curl.c: static int post_rpc(struct rpc_state *rpc, int stateless_connect,
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) {
++ if (stateless_connect)
+ packet_response_end(rpc->in);
-+ packet_flush(rpc->in);
-+ }
+
curl_slist_free_all(headers);
free(gzip_body);-- 2.26.2.706.g87896c9627