receive-pack: allow a maximum input size to be specified

Receive-pack feeds its input to either index-pack or
unpack-objects, which will happily accept as many bytes as
a sender is willing to provide. Let's allow an arbitrary
cutoff point where we will stop writing bytes to disk.

Cleaning up what has already been written to disk is a
related problem that is not addressed by this patch.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -2517,6 +2517,12 @@ receive.unpackLimit::
 	especially on slow filesystems.  If not set, the value of
 	`transfer.unpackLimit` is used instead.
 
+receive.maxInputSize::
+	If the size of the incoming pack stream is larger than this
+	limit, then git-receive-pack will error out, instead of
+	accepting the pack file. If not set or set to 0, then the size
+	is unlimited.
+
 receive.denyDeletes::
 	If set to true, git-receive-pack will deny a ref update that deletes
 	the ref. Use this to prevent such a ref deletion via a push.

Documentation/git-receive-pack.txt

@@ -33,6 +33,9 @@ post-update hooks found in the Documentation/howto directory.
 option, which tells it if updates to a ref should be denied if they
 are not fast-forwards.
 
+A number of other receive.* config options are available to tweak
+its behavior, see linkgit:git-config[1].
+
 OPTIONS
 -------
 <directory>::

builtin/receive-pack.c

@@ -46,6 +46,7 @@ static int transfer_unpack_limit = -1;
 static int advertise_atomic_push = 1;
 static int advertise_push_options;
 static int unpack_limit = 100;
+static off_t max_input_size;
 static int report_status;
 static int use_sideband;
 static int use_atomic;
@@ -212,6 +213,11 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (strcmp(var, "receive.maxinputsize") == 0) {
+		max_input_size = git_config_int64(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
@@ -1648,6 +1654,9 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 		if (fsck_objects)
 			argv_array_pushf(&child.args, "--strict%s",
 				fsck_msg_types.buf);
+		if (max_input_size)
+			argv_array_pushf(&child.args, "--max-input-size=%"PRIuMAX,
+				(uintmax_t)max_input_size);
 		child.no_stdout = 1;
 		child.err = err_fd;
 		child.git_cmd = 1;
@@ -1676,6 +1685,9 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 				fsck_msg_types.buf);
 		if (!reject_thin)
 			argv_array_push(&child.args, "--fix-thin");
+		if (max_input_size)
+			argv_array_pushf(&child.args, "--max-input-size=%"PRIuMAX,
+				(uintmax_t)max_input_size);
 		child.out = -1;
 		child.err = err_fd;
 		child.git_cmd = 1;

t/t5546-receive-limits.sh

@@ -0,0 +1,55 @@
+#!/bin/sh
+
+test_description='check receive input limits'
+. ./test-lib.sh
+
+# Let's run tests with different unpack limits: 1 and 10000
+# When the limit is 1, `git receive-pack` will call `git index-pack`.
+# When the limit is 10000, `git receive-pack` will call `git unpack-objects`.
+
+test_pack_input_limit () {
+	case "$1" in
+	index) unpack_limit=1 ;;
+	unpack) unpack_limit=10000 ;;
+	esac
+
+	test_expect_success 'prepare destination repository' '
+		rm -fr dest &&
+		git --bare init dest
+	'
+
+	test_expect_success "set unpacklimit to $unpack_limit" '
+		git --git-dir=dest config receive.unpacklimit "$unpack_limit"
+	'
+
+	test_expect_success 'setting receive.maxInputSize to 512 rejects push' '
+		git --git-dir=dest config receive.maxInputSize 512 &&
+		test_must_fail git push dest HEAD
+	'
+
+	test_expect_success 'bumping limit to 4k allows push' '
+		git --git-dir=dest config receive.maxInputSize 4k &&
+		git push dest HEAD
+	'
+
+	test_expect_success 'prepare destination repository (again)' '
+		rm -fr dest &&
+		git --bare init dest
+	'
+
+	test_expect_success 'lifting the limit allows push' '
+		git --git-dir=dest config receive.maxInputSize 0 &&
+		git push dest HEAD
+	'
+}
+
+test_expect_success "create known-size (1024 bytes) commit" '
+	test-genrandom foo 1024 >one-k &&
+	git add one-k &&
+	test_commit one-k
+'
+
+test_pack_input_limit index
+test_pack_input_limit unpack
+
+test_done