Revision 7b70e9efb18c2cc3f219af399bd384c5801ba1d7 authored by Jeff King on 16 April 2024, 08:35:33 UTC, committed by Johannes Schindelin on 17 April 2024, 20:29:56 UTC
The upload-pack command tries to avoid trusting the repository in which it's run (e.g., by not running any hooks and not using any config that contains arbitrary commands). But if the server side of a fetch or a clone is a partial clone, then either upload-pack or its child pack-objects may run a lazy "git fetch" under the hood. And it is very easy to convince fetch to run arbitrary commands. The "server" side can be a local repository owned by someone else, who would be able to configure commands that are run during a clone with the current user's permissions. This issue has been designated CVE-2024-32004. The fix in this commit's parent helps in this scenario, as well as in related scenarios using SSH to clone, where the untrusted .git directory is owned by a different user id. But if you received one as a zip file, on a USB stick, etc, it may be owned by your user but still untrusted. This has been designated CVE-2024-32465. To mitigate the issue more completely, let's disable lazy fetching entirely during `upload-pack`. While fetching from a partial repository should be relatively rare, it is certainly not an unreasonable workflow. And thus we need to provide an escape hatch. This commit works by respecting a GIT_NO_LAZY_FETCH environment variable (to skip the lazy-fetch), and setting it in upload-pack, but only when the user has not already done so (which gives us the escape hatch). The name of the variable is specifically chosen to match what has already been added in 'master' via e6d5479e7a (git: extend --no-lazy-fetch to work across subprocesses, 2024-02-27). Since we're building this fix as a backport for older versions, we could cherry-pick that patch and its earlier steps. However, we don't really need the niceties (like a "--no-lazy-fetch" option) that it offers. By using the same name, everything should just work when the two are eventually merged, but here are a few notes: - the blocking of the fetch in e6d5479e7a is incomplete! It sets fetch_if_missing to 0 when we setup the repository variable, but that isn't enough. pack-objects in particular will call prefetch_to_pack() even if that variable is 0. This patch by contrast checks the environment variable at the lowest level before we call the lazy fetch, where we can be sure to catch all code paths. Possibly the setting of fetch_if_missing from e6d5479e7a can be reverted, but it may be useful to have. For example, some code may want to use that flag to change behavior before it gets to the point of trying to start the fetch. At any rate, that's all outside the scope of this patch. - there's documentation for GIT_NO_LAZY_FETCH in e6d5479e7a. We can live without that here, because for the most part the user shouldn't need to set it themselves. The exception is if they do want to override upload-pack's default, and that requires a separate documentation section (which is added here) - it would be nice to use the NO_LAZY_FETCH_ENVIRONMENT macro added by e6d5479e7a, but those definitions have moved from cache.h to environment.h between 2.39.3 and master. I just used the raw string literals, and we can replace them with the macro once this topic is merged to master. At least with respect to CVE-2024-32004, this does render this commit's parent commit somewhat redundant. However, it is worth retaining that commit as defense in depth, and because it may help other issues (e.g., symlink/hardlink TOCTOU races, where zip files are not really an interesting attack vector). The tests in t0411 still pass, but now we have _two_ mechanisms ensuring that the evil command is not run. Let's beef up the existing ones to check that they failed for the expected reason, that we refused to run upload-pack at all with an alternate user id. And add two new ones for the same-user case that both the restriction and its escape hatch. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
1 parent f4aa8c8
trace.c
/*
* GIT - The information manager from hell
*
* Copyright (C) 2000-2002 Michael R. Elkins <me@mutt.org>
* Copyright (C) 2002-2004 Oswald Buddenhagen <ossi@users.sf.net>
* Copyright (C) 2004 Theodore Y. Ts'o <tytso@mit.edu>
* Copyright (C) 2006 Mike McCormack
* Copyright (C) 2006 Christian Couder
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "cache.h"
#include "quote.h"
struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
struct trace_key trace_setup_key = TRACE_KEY_INIT(SETUP);
/* Get a trace file descriptor from "key" env variable. */
static int get_trace_fd(struct trace_key *key, const char *override_envvar)
{
const char *trace;
/* don't open twice */
if (key->initialized)
return key->fd;
trace = override_envvar ? override_envvar : getenv(key->key);
if (!trace || !strcmp(trace, "") ||
!strcmp(trace, "0") || !strcasecmp(trace, "false"))
key->fd = 0;
else if (!strcmp(trace, "1") || !strcasecmp(trace, "true"))
key->fd = STDERR_FILENO;
else if (strlen(trace) == 1 && isdigit(*trace))
key->fd = atoi(trace);
else if (is_absolute_path(trace)) {
int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
if (fd == -1) {
warning("could not open '%s' for tracing: %s",
trace, strerror(errno));
trace_disable(key);
} else {
key->fd = fd;
key->need_close = 1;
}
} else {
warning("unknown trace value for '%s': %s\n"
" If you want to trace into a file, then please set %s\n"
" to an absolute pathname (starting with /)",
key->key, trace, key->key);
trace_disable(key);
}
key->initialized = 1;
return key->fd;
}
void trace_override_envvar(struct trace_key *key, const char *value)
{
trace_disable(key);
key->initialized = 0;
/*
* Invoke get_trace_fd() to initialize key using the given value
* instead of the value of the environment variable.
*/
get_trace_fd(key, value);
}
void trace_disable(struct trace_key *key)
{
if (key->need_close)
close(key->fd);
key->fd = 0;
key->initialized = 1;
key->need_close = 0;
}
static int prepare_trace_line(const char *file, int line,
struct trace_key *key, struct strbuf *buf)
{
static struct trace_key trace_bare = TRACE_KEY_INIT(BARE);
struct timeval tv;
struct tm tm;
time_t secs;
if (!trace_want(key))
return 0;
/* unit tests may want to disable additional trace output */
if (trace_want(&trace_bare))
return 1;
/* print current timestamp */
gettimeofday(&tv, NULL);
secs = tv.tv_sec;
localtime_r(&secs, &tm);
strbuf_addf(buf, "%02d:%02d:%02d.%06ld %s:%d", tm.tm_hour, tm.tm_min,
tm.tm_sec, (long) tv.tv_usec, file, line);
/* align trace output (column 40 catches most files names in git) */
while (buf->len < 40)
strbuf_addch(buf, ' ');
return 1;
}
static void trace_write(struct trace_key *key, const void *buf, unsigned len)
{
if (write_in_full(get_trace_fd(key, NULL), buf, len) < 0) {
warning("unable to write trace for %s: %s",
key->key, strerror(errno));
trace_disable(key);
}
}
void trace_verbatim(struct trace_key *key, const void *buf, unsigned len)
{
if (!trace_want(key))
return;
trace_write(key, buf, len);
}
static void print_trace_line(struct trace_key *key, struct strbuf *buf)
{
strbuf_complete_line(buf);
trace_write(key, buf->buf, buf->len);
}
static void trace_vprintf_fl(const char *file, int line, struct trace_key *key,
const char *format, va_list ap)
{
struct strbuf buf = STRBUF_INIT;
if (!prepare_trace_line(file, line, key, &buf))
return;
strbuf_vaddf(&buf, format, ap);
print_trace_line(key, &buf);
strbuf_release(&buf);
}
static void trace_argv_vprintf_fl(const char *file, int line,
const char **argv, const char *format,
va_list ap)
{
struct strbuf buf = STRBUF_INIT;
if (!prepare_trace_line(file, line, &trace_default_key, &buf))
return;
strbuf_vaddf(&buf, format, ap);
sq_quote_argv_pretty(&buf, argv);
print_trace_line(&trace_default_key, &buf);
strbuf_release(&buf);
}
void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
const struct strbuf *data)
{
struct strbuf buf = STRBUF_INIT;
if (!prepare_trace_line(file, line, key, &buf))
return;
strbuf_addbuf(&buf, data);
print_trace_line(key, &buf);
strbuf_release(&buf);
}
static uint64_t perf_start_times[10];
static int perf_indent;
uint64_t trace_performance_enter(void)
{
uint64_t now;
if (!trace_want(&trace_perf_key))
return 0;
now = getnanotime();
perf_start_times[perf_indent] = now;
if (perf_indent + 1 < ARRAY_SIZE(perf_start_times))
perf_indent++;
else
BUG("Too deep indentation");
return now;
}
static void trace_performance_vprintf_fl(const char *file, int line,
uint64_t nanos, const char *format,
va_list ap)
{
static const char space[] = " ";
struct strbuf buf = STRBUF_INIT;
if (!prepare_trace_line(file, line, &trace_perf_key, &buf))
return;
strbuf_addf(&buf, "performance: %.9f s", (double) nanos / 1000000000);
if (format && *format) {
if (perf_indent >= strlen(space))
BUG("Too deep indentation");
strbuf_addf(&buf, ":%.*s ", perf_indent, space);
strbuf_vaddf(&buf, format, ap);
}
print_trace_line(&trace_perf_key, &buf);
strbuf_release(&buf);
}
void trace_printf_key_fl(const char *file, int line, struct trace_key *key,
const char *format, ...)
{
va_list ap;
va_start(ap, format);
trace_vprintf_fl(file, line, key, format, ap);
va_end(ap);
}
void trace_argv_printf_fl(const char *file, int line, const char **argv,
const char *format, ...)
{
va_list ap;
va_start(ap, format);
trace_argv_vprintf_fl(file, line, argv, format, ap);
va_end(ap);
}
void trace_performance_fl(const char *file, int line, uint64_t nanos,
const char *format, ...)
{
va_list ap;
va_start(ap, format);
trace_performance_vprintf_fl(file, line, nanos, format, ap);
va_end(ap);
}
void trace_performance_leave_fl(const char *file, int line,
uint64_t nanos, const char *format, ...)
{
va_list ap;
uint64_t since;
if (perf_indent)
perf_indent--;
if (!format) /* Allow callers to leave without tracing anything */
return;
since = perf_start_times[perf_indent];
va_start(ap, format);
trace_performance_vprintf_fl(file, line, nanos - since, format, ap);
va_end(ap);
}
static const char *quote_crnl(const char *path)
{
static struct strbuf new_path = STRBUF_INIT;
if (!path)
return NULL;
strbuf_reset(&new_path);
while (*path) {
switch (*path) {
case '\\': strbuf_addstr(&new_path, "\\\\"); break;
case '\n': strbuf_addstr(&new_path, "\\n"); break;
case '\r': strbuf_addstr(&new_path, "\\r"); break;
default:
strbuf_addch(&new_path, *path);
}
path++;
}
return new_path.buf;
}
/* FIXME: move prefix to startup_info struct and get rid of this arg */
void trace_repo_setup(const char *prefix)
{
const char *git_work_tree;
char *cwd;
if (!trace_want(&trace_setup_key))
return;
cwd = xgetcwd();
if (!(git_work_tree = get_git_work_tree()))
git_work_tree = "(null)";
if (!prefix)
prefix = "(null)";
trace_printf_key(&trace_setup_key, "setup: git_dir: %s\n", quote_crnl(get_git_dir()));
trace_printf_key(&trace_setup_key, "setup: git_common_dir: %s\n", quote_crnl(get_git_common_dir()));
trace_printf_key(&trace_setup_key, "setup: worktree: %s\n", quote_crnl(git_work_tree));
trace_printf_key(&trace_setup_key, "setup: cwd: %s\n", quote_crnl(cwd));
trace_printf_key(&trace_setup_key, "setup: prefix: %s\n", quote_crnl(prefix));
free(cwd);
}
int trace_want(struct trace_key *key)
{
return !!get_trace_fd(key, NULL);
}
#if defined(HAVE_CLOCK_GETTIME) && defined(HAVE_CLOCK_MONOTONIC)
static inline uint64_t highres_nanos(void)
{
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts))
return 0;
return (uint64_t) ts.tv_sec * 1000000000 + ts.tv_nsec;
}
#elif defined (GIT_WINDOWS_NATIVE)
static inline uint64_t highres_nanos(void)
{
static uint64_t high_ns, scaled_low_ns;
static int scale;
LARGE_INTEGER cnt;
if (!scale) {
if (!QueryPerformanceFrequency(&cnt))
return 0;
/* high_ns = number of ns per cnt.HighPart */
high_ns = (1000000000LL << 32) / (uint64_t) cnt.QuadPart;
/*
* Number of ns per cnt.LowPart is 10^9 / frequency (or
* high_ns >> 32). For maximum precision, we scale this factor
* so that it just fits within 32 bit (i.e. won't overflow if
* multiplied with cnt.LowPart).
*/
scaled_low_ns = high_ns;
scale = 32;
while (scaled_low_ns >= 0x100000000LL) {
scaled_low_ns >>= 1;
scale--;
}
}
/* if QPF worked on initialization, we expect QPC to work as well */
QueryPerformanceCounter(&cnt);
return (high_ns * cnt.HighPart) +
((scaled_low_ns * cnt.LowPart) >> scale);
}
#else
# define highres_nanos() 0
#endif
static inline uint64_t gettimeofday_nanos(void)
{
struct timeval tv;
gettimeofday(&tv, NULL);
return (uint64_t) tv.tv_sec * 1000000000 + tv.tv_usec * 1000;
}
/*
* Returns nanoseconds since the epoch (01/01/1970), for performance tracing
* (i.e. favoring high precision over wall clock time accuracy).
*/
uint64_t getnanotime(void)
{
static uint64_t offset;
if (offset > 1) {
/* initialization succeeded, return offset + high res time */
return offset + highres_nanos();
} else if (offset == 1) {
/* initialization failed, fall back to gettimeofday */
return gettimeofday_nanos();
} else {
/* initialize offset if high resolution timer works */
uint64_t now = gettimeofday_nanos();
uint64_t highres = highres_nanos();
if (highres)
offset = now - highres;
else
offset = 1;
return now;
}
}
static struct strbuf command_line = STRBUF_INIT;
static void print_command_performance_atexit(void)
{
trace_performance_leave("git command:%s", command_line.buf);
}
void trace_command_performance(const char **argv)
{
if (!trace_want(&trace_perf_key))
return;
if (!command_line.len)
atexit(print_command_performance_atexit);
strbuf_reset(&command_line);
sq_quote_argv_pretty(&command_line, argv);
trace_performance_enter();
}
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