[PATCH 6/9] upload-pack: disallow object-info capability by default
- From
Jeff King <peff@peff.net>
- Date
- Feb 28, 2024, 22:38 UTC
- Message-ID
- <20240228223858.GF1158131@coredump.intra.peff.net>
- In-Reply-To
- <20240228223700.GA1157826@coredump.intra.peff.net>
From: Taylor Blau <me@ttaylorr.com>
We added an "object-info" capability to the v2 upload-pack protocol in a2ba162cda (object-info: support for retrieving object info, 2021-04-20). In the almost 3 years since, we have not added any client-side support, and it does not appear to exist in other implementations either (JGit understands the verb on the server side, but not on the client side).
Since this largely unused code is accessible over the network by default, it increases the attack surface of upload-pack. I don't know of any particularly severe problem, but one issue is that because of the request/response nature of the v2 protocol, it will happily read an unbounded number of packets, adding each one to a string list (without regard to whether they are objects we know about, duplicates, etc).
This may be something we want to improve in the long run, but in the short term it makes sense to disable the feature entirely. We'll add a config option as an escape hatch for anybody who wants to develop the feature further.
A more gentle option would be to add the config option to let people disable it manually, but leave it enabled by default. But given that there's no client side support, that seems like the wrong balance with security.
Disabling by default will slow adoption a bit once client-side support does become available (there were some patches[1] in 2022, but nothing got merged and there's been nothing since). But clients have to deal with older servers that do not understand the option anyway (and the capability system handles that), so it will just be a matter of servers flipping their config at that point (and hopefully once any unbounded allocations have been addressed).
[jk: this is a patch that GitHub has been running for several years, but
rebased forward and with a new commit message for upstream][1] https://lore.kernel.org/git/20220208231911.725273-1-calvinwan@google.com/
Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Jeff King <peff@peff.net> --- Documentation/config/transfer.txt | 4 ++++ serve.c | 14 +++++++++++++- t/t5555-http-smart-common.sh | 1 - t/t5701-git-serve.sh | 24 +++++++++++++++++++++++- 4 files changed, 40 insertions(+), 3 deletions(-)
diff --git a/Documentation/config/transfer.txt b/Documentation/config/transfer.txt index a9cbdb88a1..f1ce50f4a6 100644 --- a/Documentation/config/transfer.txt +++ b/Documentation/config/transfer.txt @@ -121,3 +121,7 @@ transfer.bundleURI:: information from the remote server (if advertised) and download bundles before continuing the clone through the Git protocol. Defaults to `false`. + +transfer.advertiseObjectInfo:: + When `true`, the `object-info` capability is advertised by + servers. Defaults to false. diff --git a/serve.c b/serve.c index a1d71134d4..aa651b73e9 100644 --- a/serve.c +++ b/serve.c @@ -12,6 +12,7 @@ #include "trace2.h" static int advertise_sid = -1; +static int advertise_object_info = -1; static int client_hash_algo = GIT_HASH_SHA1; static int always_advertise(struct repository *r UNUSED, @@ -67,6 +68,17 @@ static void session_id_receive(struct repository *r UNUSED, trace2_data_string("transfer", NULL, "client-sid", client_sid); } +static int object_info_advertise(struct repository *r, struct strbuf *value UNUSED) +{ + if (advertise_object_info == -1 && + repo_config_get_bool(r, "transfer.advertiseobjectinfo", + &advertise_object_info)) { + /* disabled by default */ + advertise_object_info = 0; + } + return advertise_object_info; +} + struct protocol_capability { /* * The name of the capability. The server uses this name when @@ -135,7 +147,7 @@ static struct protocol_capability capabilities[] = { }, { .name = "object-info", - .advertise = always_advertise, + .advertise = object_info_advertise, .command = cap_object_info, }, { diff --git a/t/t5555-http-smart-common.sh b/t/t5555-http-smart-common.sh index b1cfe8b7db..3dcb3340a3 100755 --- a/t/t5555-http-smart-common.sh +++ b/t/t5555-http-smart-common.sh @@ -131,7 +131,6 @@ test_expect_success 'git upload-pack --advertise-refs: v2' ' fetch=shallow wait-for-done server-option object-format=$(test_oid algo) - object-info 0000 EOF diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh index 3591bc2417..c48830de8f 100755 --- a/t/t5701-git-serve.sh +++ b/t/t5701-git-serve.sh @@ -20,7 +20,6 @@ test_expect_success 'test capability advertisement' ' fetch=shallow wait-for-done server-option object-format=$(test_oid algo) - object-info EOF cat >expect.trailer <<-EOF && 0000 @@ -323,6 +322,8 @@ test_expect_success 'unexpected lines are not allowed in fetch request' ' # Test the basics of object-info # test_expect_success 'basics of object-info' ' + test_config transfer.advertiseObjectInfo true && + test-tool pkt-line pack >in <<-EOF && command=object-info object-format=$(test_oid algo) @@ -380,4 +381,25 @@ test_expect_success 'basics of bundle-uri: dies if not enabled' ' test_must_be_empty out ' +test_expect_success 'object-info missing from capabilities when disabled' ' + test_config transfer.advertiseObjectInfo false && + + GIT_TEST_SIDEBAND_ALL=0 test-tool serve-v2 \ + --advertise-capabilities >out && + test-tool pkt-line unpack <out >actual && + + ! grep object.info actual +' + +test_expect_success 'object-info commands rejected when disabled' ' + test_config transfer.advertiseObjectInfo false && + + test-tool pkt-line pack >in <<-EOF && + command=object-info + EOF + + test_must_fail test-tool serve-v2 --stateless-rpc <in 2>err && + grep invalid.command err +' + test_done
-- 2.44.0.rc2.424.gbdbf4d014b