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
sideband.c
#include "cache.h"
#include "color.h"
#include "config.h"
#include "sideband.h"
#include "help.h"
#include "pkt-line.h"
struct keyword_entry {
/*
* We use keyword as config key so it should be a single alphanumeric word.
*/
const char *keyword;
char color[COLOR_MAXLEN];
};
static struct keyword_entry keywords[] = {
{ "hint", GIT_COLOR_YELLOW },
{ "warning", GIT_COLOR_BOLD_YELLOW },
{ "success", GIT_COLOR_BOLD_GREEN },
{ "error", GIT_COLOR_BOLD_RED },
};
/* Returns a color setting (GIT_COLOR_NEVER, etc). */
static int use_sideband_colors(void)
{
static int use_sideband_colors_cached = -1;
const char *key = "color.remote";
struct strbuf sb = STRBUF_INIT;
char *value;
int i;
if (use_sideband_colors_cached >= 0)
return use_sideband_colors_cached;
if (!git_config_get_string(key, &value)) {
use_sideband_colors_cached = git_config_colorbool(key, value);
} else if (!git_config_get_string("color.ui", &value)) {
use_sideband_colors_cached = git_config_colorbool("color.ui", value);
} else {
use_sideband_colors_cached = GIT_COLOR_AUTO;
}
for (i = 0; i < ARRAY_SIZE(keywords); i++) {
strbuf_reset(&sb);
strbuf_addf(&sb, "%s.%s", key, keywords[i].keyword);
if (git_config_get_string(sb.buf, &value))
continue;
if (color_parse(value, keywords[i].color))
continue;
}
strbuf_release(&sb);
return use_sideband_colors_cached;
}
void list_config_color_sideband_slots(struct string_list *list, const char *prefix)
{
int i;
for (i = 0; i < ARRAY_SIZE(keywords); i++)
list_config_item(list, prefix, keywords[i].keyword);
}
/*
* Optionally highlight one keyword in remote output if it appears at the start
* of the line. This should be called for a single line only, which is
* passed as the first N characters of the SRC array.
*
* NEEDSWORK: use "size_t n" instead for clarity.
*/
static void maybe_colorize_sideband(struct strbuf *dest, const char *src, int n)
{
int i;
if (!want_color_stderr(use_sideband_colors())) {
strbuf_add(dest, src, n);
return;
}
while (0 < n && isspace(*src)) {
strbuf_addch(dest, *src);
src++;
n--;
}
for (i = 0; i < ARRAY_SIZE(keywords); i++) {
struct keyword_entry *p = keywords + i;
int len = strlen(p->keyword);
if (n < len)
continue;
/*
* Match case insensitively, so we colorize output from existing
* servers regardless of the case that they use for their
* messages. We only highlight the word precisely, so
* "successful" stays uncolored.
*/
if (!strncasecmp(p->keyword, src, len) &&
(len == n || !isalnum(src[len]))) {
strbuf_addstr(dest, p->color);
strbuf_add(dest, src, len);
strbuf_addstr(dest, GIT_COLOR_RESET);
n -= len;
src += len;
break;
}
}
strbuf_add(dest, src, n);
}
#define DISPLAY_PREFIX "remote: "
#define ANSI_SUFFIX "\033[K"
#define DUMB_SUFFIX " "
int demultiplex_sideband(const char *me, int status,
char *buf, int len,
int die_on_error,
struct strbuf *scratch,
enum sideband_type *sideband_type)
{
static const char *suffix;
const char *b, *brk;
int band;
if (!suffix) {
if (isatty(2) && !is_terminal_dumb())
suffix = ANSI_SUFFIX;
else
suffix = DUMB_SUFFIX;
}
if (status == PACKET_READ_EOF) {
strbuf_addf(scratch,
"%s%s: unexpected disconnect while reading sideband packet",
scratch->len ? "\n" : "", me);
*sideband_type = SIDEBAND_PROTOCOL_ERROR;
goto cleanup;
}
if (len < 0)
BUG("negative length on non-eof packet read");
if (len == 0) {
if (status == PACKET_READ_NORMAL) {
strbuf_addf(scratch,
"%s%s: protocol error: missing sideband designator",
scratch->len ? "\n" : "", me);
*sideband_type = SIDEBAND_PROTOCOL_ERROR;
} else {
/* covers flush, delim, etc */
*sideband_type = SIDEBAND_FLUSH;
}
goto cleanup;
}
band = buf[0] & 0xff;
buf[len] = '\0';
len--;
switch (band) {
case 3:
if (die_on_error)
die(_("remote error: %s"), buf + 1);
strbuf_addf(scratch, "%s%s", scratch->len ? "\n" : "",
DISPLAY_PREFIX);
maybe_colorize_sideband(scratch, buf + 1, len);
*sideband_type = SIDEBAND_REMOTE_ERROR;
break;
case 2:
b = buf + 1;
/*
* Append a suffix to each nonempty line to clear the
* end of the screen line.
*
* The output is accumulated in a buffer and
* each line is printed to stderr using
* write(2) to ensure inter-process atomicity.
*/
while ((brk = strpbrk(b, "\n\r"))) {
int linelen = brk - b;
/*
* For message accross packet boundary, there would have
* a nonempty "scratch" buffer from last call of this
* function, and there may have a leading CR/LF in "buf".
* For this case we should add a clear-to-eol suffix to
* clean leftover letters we previously have written on
* the same line.
*/
if (scratch->len && !linelen)
strbuf_addstr(scratch, suffix);
if (!scratch->len)
strbuf_addstr(scratch, DISPLAY_PREFIX);
/*
* A use case that we should not add clear-to-eol suffix
* to empty lines:
*
* For progress reporting we may receive a bunch of
* percentage updates followed by '\r' to remain on the
* same line, and at the end receive a single '\n' to
* move to the next line. We should preserve the final
* status report line by not appending clear-to-eol
* suffix to this single line break.
*/
if (linelen > 0) {
maybe_colorize_sideband(scratch, b, linelen);
strbuf_addstr(scratch, suffix);
}
strbuf_addch(scratch, *brk);
xwrite(2, scratch->buf, scratch->len);
strbuf_reset(scratch);
b = brk + 1;
}
if (*b) {
strbuf_addstr(scratch, scratch->len ?
"" : DISPLAY_PREFIX);
maybe_colorize_sideband(scratch, b, strlen(b));
}
return 0;
case 1:
*sideband_type = SIDEBAND_PRIMARY;
return 1;
default:
strbuf_addf(scratch, "%s%s: protocol error: bad band #%d",
scratch->len ? "\n" : "", me, band);
*sideband_type = SIDEBAND_PROTOCOL_ERROR;
break;
}
cleanup:
if (die_on_error && *sideband_type == SIDEBAND_PROTOCOL_ERROR)
die("%s", scratch->buf);
if (scratch->len) {
strbuf_addch(scratch, '\n');
xwrite(2, scratch->buf, scratch->len);
}
strbuf_release(scratch);
return 1;
}
/*
* fd is connected to the remote side; send the sideband data
* over multiplexed packet stream.
*/
void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_max)
{
const char *p = data;
while (sz) {
unsigned n;
char hdr[5];
n = sz;
if (packet_max - 5 < n)
n = packet_max - 5;
if (0 <= band) {
xsnprintf(hdr, sizeof(hdr), "%04x", n + 5);
hdr[4] = band;
write_or_die(fd, hdr, 5);
} else {
xsnprintf(hdr, sizeof(hdr), "%04x", n + 4);
write_or_die(fd, hdr, 4);
}
write_or_die(fd, p, n);
p += n;
sz -= n;
}
}
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