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Revision 24557209500e6ed618f04a8795a111a0c491a29c authored by Patrick Steinhardt on 01 December 2022, 14:45:23 UTC, committed by Junio C Hamano on 05 December 2022, 06:14:16 UTC 
attr: fix integer overflow when parsing huge attribute names
 
It is possible to trigger an integer overflow when parsing attribute
names that are longer than 2^31 bytes because we assign the result of
strlen(3P) to an `int` instead of to a `size_t`. This can lead to an
abort in vsnprintf(3P) with the following reproducer:

    blob=$(perl -e 'print "A " . "B"x2147483648 . "\n"' | git hash-object -w --stdin)
    git update-index --add --cacheinfo 100644,$blob,.gitattributes
    git check-attr --all path

    BUG: strbuf.c:400: your vsnprintf is broken (returned -1)

But furthermore, assuming that the attribute name is even longer than
that, it can cause us to silently truncate the attribute and thus lead
to wrong results.

Fix this integer overflow by using a `size_t` instead. This fixes the
silent truncation of attribute names, but it only partially fixes the
BUG we hit: even though the initial BUG is fixed, we can still hit a BUG
when parsing invalid attribute lines via `report_invalid_attr()`.

This is due to an underlying design issue in vsnprintf(3P) which only
knows to return an `int`, and thus it may always overflow with large
inputs. This issue is benign though: the worst that can happen is that
the error message is misreported to be either truncated or too long, but
due to the buffer being NUL terminated we wouldn't ever do an
out-of-bounds read here.

Reported-by: Markus Vervier <markus.vervier@x41-dsec.de>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 parent 8d0d48c
Raw File
protocol.c 
#include "cache.h"
#include "config.h"
#include "protocol.h"

static enum protocol_version parse_protocol_version(const char *value)
{
	if (!strcmp(value, "0"))
		return protocol_v0;
	else if (!strcmp(value, "1"))
		return protocol_v1;
	else if (!strcmp(value, "2"))
		return protocol_v2;
	else
		return protocol_unknown_version;
}

enum protocol_version get_protocol_version_config(void)
{
	const char *value;
	const char *git_test_k = "GIT_TEST_PROTOCOL_VERSION";
	const char *git_test_v;

	if (!git_config_get_string_tmp("protocol.version", &value)) {
		enum protocol_version version = parse_protocol_version(value);

		if (version == protocol_unknown_version)
			die("unknown value for config 'protocol.version': %s",
			    value);

		return version;
	}

	git_test_v = getenv(git_test_k);
	if (git_test_v && *git_test_v) {
		enum protocol_version env = parse_protocol_version(git_test_v);

		if (env == protocol_unknown_version)
			die("unknown value for %s: %s", git_test_k, git_test_v);
		return env;
	}

	return protocol_v2;
}

enum protocol_version determine_protocol_version_server(void)
{
	const char *git_protocol = getenv(GIT_PROTOCOL_ENVIRONMENT);
	enum protocol_version version = protocol_v0;

	/*
	 * Determine which protocol version the client has requested.  Since
	 * multiple 'version' keys can be sent by the client, indicating that
	 * the client is okay to speak any of them, select the greatest version
	 * that the client has requested.  This is due to the assumption that
	 * the most recent protocol version will be the most state-of-the-art.
	 */
	if (git_protocol) {
		struct string_list list = STRING_LIST_INIT_DUP;
		const struct string_list_item *item;
		string_list_split(&list, git_protocol, ':', -1);

		for_each_string_list_item(item, &list) {
			const char *value;
			enum protocol_version v;

			if (skip_prefix(item->string, "version=", &value)) {
				v = parse_protocol_version(value);
				if (v > version)
					version = v;
			}
		}

		string_list_clear(&list, 0);
	}

	return version;
}

enum protocol_version determine_protocol_version_client(const char *server_response)
{
	enum protocol_version version = protocol_v0;

	if (skip_prefix(server_response, "version ", &server_response)) {
		version = parse_protocol_version(server_response);

		if (version == protocol_unknown_version)
			die("server is speaking an unknown protocol");
		if (version == protocol_v0)
			die("protocol error: server explicitly said version 0");
	}

	return version;
}
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