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upload-pack: allow stateless client EOF just prior to haves 

During stateless packfile negotiation where a depth is given, stateless
RPC clients (e.g. git-remote-curl) will send multiple upload-pack
requests with the first containing only the
wants/shallows/deepens/filters and the subsequent containing haves/done.

When upload-pack handles such requests, entering get_common_commits
without checking whether the client has hung up can result in unexpected
EOF during the negotiation loop and a die() with message "fatal: the
remote end hung up unexpectedly".

Real world effects include:

 - A client speaking to git-http-backend via a server that doesn't check
   the exit codes of CGIs (e.g. mod_cgi) doesn't know and doesn't care
   about the fatal. It continues to process the response body as normal.

 - A client speaking to a server that does check the exit code and
   returns an errant HTTP status as a result will fail with the message
   "error: RPC failed; HTTP 500 curl 22 The requested URL returned error:
   500."

 - Admins running servers that surface the failure must workaround it by
   patching code that handles execution of git-http-backend to ignore exit
   codes or take other heuristic approaches.

 - Admins may have to deal with "hung up unexpectedly" log spam related
   to the failures even in cases where the exit code isn't surfaced as an
   HTTP server-side error status.

To avoid these EOF related fatals, have upload-pack gently peek for an
EOF between the sending of shallow/unshallow lines (followed by flush)
and the reading of client haves. If the client has hung up at this
point, exit normally.

Signed-off-by: Daniel Duvall <dan@mutual.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Daniel Duvall 2020-10-30 19:39:02 -07:00 committed by Junio C Hamano
parent e2850a27a9
commit fb3d1a083f
2 changed files with 29 additions and 1 deletions
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17
t/t5530-upload-pack-error.sh
View File

@ -88,6 +88,23 @@ test_expect_success 'upload-pack fails due to error in pack-objects enumeration'
grep "pack-objects died" output.err
'
test_expect_success 'upload-pack tolerates EOF just after stateless client wants' '
test_commit initial &&
head=$(git rev-parse HEAD) &&
{
packetize "want $head" &&
packetize "shallow $head" &&
packetize "deepen 1" &&
printf "0000"
} >request &&
printf "0000" >expect &&
git upload-pack --stateless-rpc . <request >actual &&
test_cmp expect actual
'
test_expect_success 'create empty repository' '
mkdir foo &&

13
upload-pack.c
View File

@ -1344,7 +1344,18 @@ void upload_pack(struct upload_pack_options *options)
PACKET_READ_DIE_ON_ERR_PACKET);
receive_needs(&data, &reader);
if (data.want_obj.nr) {
/*
* An EOF at this exact point in negotiation should be
* acceptable from stateless clients as they will consume the
* shallow list before doing subsequent rpc with haves/etc.
*/
if (data.stateless_rpc)
reader.options |= PACKET_READ_GENTLE_ON_EOF;
if (data.want_obj.nr &&
packet_reader_peek(&reader) != PACKET_READ_EOF) {
reader.options &= ~PACKET_READ_GENTLE_ON_EOF;
get_common_commits(&data, &reader);
create_pack_file(&data, NULL);
}