[PATCH 3/3] receive-pack: allow a maximum input size to be specified

[Christian Couder <christian.couder@gmail.com>]

From: Jeff King <peff@peff.net>

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.

The problem is that git-gc can clean up tmp_pack_* files
after their grace time expired, but that may not be
enough if someone tries to "git push" in a loop.

A simple fix is to call register_tempfile() in
open_pack_file(), and just have index-pack clean up the
file on its way out.

But there are harder cases. For instance, if somebody
pushes a 500MB file, and there is a pre-receive hook that
says "too big; I won't accept this". And then they push in
a loop, the incoming pack has already been accepted into
the repository by the time the pre-receive hook runs.
It's not possible to just delete it, because we don't know
if other simultaneous processes have started to depend on
the objects.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 Documentation/config.txt           |  5 +++++
 Documentation/git-receive-pack.txt |  3 +++
 builtin/receive-pack.c             | 12 +++++++++++
 t/t5546-push-limits.sh             | 42 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+)
 create mode 100755 t/t5546-push-limits.sh

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 0bcb679..f5b6061 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2517,6 +2517,11 @@ receive.unpackLimit::
 	especially on slow filesystems.  If not set, the value of
 	`transfer.unpackLimit` is used instead.
 
+receive.maxsize::
+	If the size of a pack file 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.
diff --git a/Documentation/git-receive-pack.txt b/Documentation/git-receive-pack.txt
index 000ee8d..0ccd5fb 100644
--- a/Documentation/git-receive-pack.txt
+++ b/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>::
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 92e1213..8c2943d 100644
--- a/builtin/receive-pack.c
+++ b/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.maxsize") == 0) {
+		max_input_size = git_config_int64(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
@@ -1650,6 +1656,9 @@ 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;
@@ -1678,6 +1687,9 @@ 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;
diff --git a/t/t5546-push-limits.sh b/t/t5546-push-limits.sh
new file mode 100755
index 0000000..b38d508
--- /dev/null
+++ b/t/t5546-push-limits.sh
@@ -0,0 +1,42 @@
+#!/bin/sh
+
+test_description='check input limits for pushing'
+. ./test-lib.sh
+
+test_expect_success 'create remote repository' '
+	git init --bare dest
+'
+
+# Let's run tests with different unpack limits: 1 and 10
+# When the limit is 1, `git receive-pack` will call `git index-pack`.
+# When the limit is 10, `git receive-pack` will call `git unpack-objects`.
+
+while read unpacklimit filesize filename
+do
+
+	test_expect_success "create known-size ($filesize bytes) commit '$filename'" '
+		test-genrandom foo "$filesize" >"$filename" &&
+		git add "$filename" &&
+		test_commit "$filename"
+	'
+
+	test_expect_success "set unpacklimit to $unpacklimit" '
+		git --git-dir=dest config receive.unpacklimit "$unpacklimit"
+	'
+
+	test_expect_success 'setting receive.maxsize to 512 rejects push' '
+		git --git-dir=dest config receive.maxsize 512 &&
+		test_must_fail git push dest HEAD
+	'
+
+	test_expect_success 'bumping limit to 4k allows push' '
+		git --git-dir=dest config receive.maxsize 4k &&
+		git push dest HEAD
+	'
+
+done <<\EOF
+1 1024 one-k-file
+10 2048 two-k-file
+EOF
+
+test_done
-- 
2.10.0.rc0.3.g8535b4c