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
streaming.c
/*
* Copyright (c) 2011, Google Inc.
*/
#include "cache.h"
#include "streaming.h"
#include "repository.h"
#include "object-store.h"
#include "replace-object.h"
#include "packfile.h"
typedef int (*open_istream_fn)(struct git_istream *,
struct repository *,
const struct object_id *,
enum object_type *);
typedef int (*close_istream_fn)(struct git_istream *);
typedef ssize_t (*read_istream_fn)(struct git_istream *, char *, size_t);
#define FILTER_BUFFER (1024*16)
struct filtered_istream {
struct git_istream *upstream;
struct stream_filter *filter;
char ibuf[FILTER_BUFFER];
char obuf[FILTER_BUFFER];
int i_end, i_ptr;
int o_end, o_ptr;
int input_finished;
};
struct git_istream {
open_istream_fn open;
close_istream_fn close;
read_istream_fn read;
unsigned long size; /* inflated size of full object */
git_zstream z;
enum { z_unused, z_used, z_done, z_error } z_state;
union {
struct {
char *buf; /* from read_object() */
unsigned long read_ptr;
} incore;
struct {
void *mapped;
unsigned long mapsize;
char hdr[32];
int hdr_avail;
int hdr_used;
} loose;
struct {
struct packed_git *pack;
off_t pos;
} in_pack;
struct filtered_istream filtered;
} u;
};
/*****************************************************************
*
* Common helpers
*
*****************************************************************/
static void close_deflated_stream(struct git_istream *st)
{
if (st->z_state == z_used)
git_inflate_end(&st->z);
}
/*****************************************************************
*
* Filtered stream
*
*****************************************************************/
static int close_istream_filtered(struct git_istream *st)
{
free_stream_filter(st->u.filtered.filter);
return close_istream(st->u.filtered.upstream);
}
static ssize_t read_istream_filtered(struct git_istream *st, char *buf,
size_t sz)
{
struct filtered_istream *fs = &(st->u.filtered);
size_t filled = 0;
while (sz) {
/* do we already have filtered output? */
if (fs->o_ptr < fs->o_end) {
size_t to_move = fs->o_end - fs->o_ptr;
if (sz < to_move)
to_move = sz;
memcpy(buf + filled, fs->obuf + fs->o_ptr, to_move);
fs->o_ptr += to_move;
sz -= to_move;
filled += to_move;
continue;
}
fs->o_end = fs->o_ptr = 0;
/* do we have anything to feed the filter with? */
if (fs->i_ptr < fs->i_end) {
size_t to_feed = fs->i_end - fs->i_ptr;
size_t to_receive = FILTER_BUFFER;
if (stream_filter(fs->filter,
fs->ibuf + fs->i_ptr, &to_feed,
fs->obuf, &to_receive))
return -1;
fs->i_ptr = fs->i_end - to_feed;
fs->o_end = FILTER_BUFFER - to_receive;
continue;
}
/* tell the filter to drain upon no more input */
if (fs->input_finished) {
size_t to_receive = FILTER_BUFFER;
if (stream_filter(fs->filter,
NULL, NULL,
fs->obuf, &to_receive))
return -1;
fs->o_end = FILTER_BUFFER - to_receive;
if (!fs->o_end)
break;
continue;
}
fs->i_end = fs->i_ptr = 0;
/* refill the input from the upstream */
if (!fs->input_finished) {
fs->i_end = read_istream(fs->upstream, fs->ibuf, FILTER_BUFFER);
if (fs->i_end < 0)
return -1;
if (fs->i_end)
continue;
}
fs->input_finished = 1;
}
return filled;
}
static struct git_istream *attach_stream_filter(struct git_istream *st,
struct stream_filter *filter)
{
struct git_istream *ifs = xmalloc(sizeof(*ifs));
struct filtered_istream *fs = &(ifs->u.filtered);
ifs->close = close_istream_filtered;
ifs->read = read_istream_filtered;
fs->upstream = st;
fs->filter = filter;
fs->i_end = fs->i_ptr = 0;
fs->o_end = fs->o_ptr = 0;
fs->input_finished = 0;
ifs->size = -1; /* unknown */
return ifs;
}
/*****************************************************************
*
* Loose object stream
*
*****************************************************************/
static ssize_t read_istream_loose(struct git_istream *st, char *buf, size_t sz)
{
size_t total_read = 0;
switch (st->z_state) {
case z_done:
return 0;
case z_error:
return -1;
default:
break;
}
if (st->u.loose.hdr_used < st->u.loose.hdr_avail) {
size_t to_copy = st->u.loose.hdr_avail - st->u.loose.hdr_used;
if (sz < to_copy)
to_copy = sz;
memcpy(buf, st->u.loose.hdr + st->u.loose.hdr_used, to_copy);
st->u.loose.hdr_used += to_copy;
total_read += to_copy;
}
while (total_read < sz) {
int status;
st->z.next_out = (unsigned char *)buf + total_read;
st->z.avail_out = sz - total_read;
status = git_inflate(&st->z, Z_FINISH);
total_read = st->z.next_out - (unsigned char *)buf;
if (status == Z_STREAM_END) {
git_inflate_end(&st->z);
st->z_state = z_done;
break;
}
if (status != Z_OK && (status != Z_BUF_ERROR || total_read < sz)) {
git_inflate_end(&st->z);
st->z_state = z_error;
return -1;
}
}
return total_read;
}
static int close_istream_loose(struct git_istream *st)
{
close_deflated_stream(st);
munmap(st->u.loose.mapped, st->u.loose.mapsize);
return 0;
}
static int open_istream_loose(struct git_istream *st, struct repository *r,
const struct object_id *oid,
enum object_type *type)
{
struct object_info oi = OBJECT_INFO_INIT;
oi.sizep = &st->size;
oi.typep = type;
st->u.loose.mapped = map_loose_object(r, oid, &st->u.loose.mapsize);
if (!st->u.loose.mapped)
return -1;
switch (unpack_loose_header(&st->z, st->u.loose.mapped,
st->u.loose.mapsize, st->u.loose.hdr,
sizeof(st->u.loose.hdr), NULL)) {
case ULHR_OK:
break;
case ULHR_BAD:
case ULHR_TOO_LONG:
goto error;
}
if (parse_loose_header(st->u.loose.hdr, &oi) < 0 || *type < 0)
goto error;
st->u.loose.hdr_used = strlen(st->u.loose.hdr) + 1;
st->u.loose.hdr_avail = st->z.total_out;
st->z_state = z_used;
st->close = close_istream_loose;
st->read = read_istream_loose;
return 0;
error:
git_inflate_end(&st->z);
munmap(st->u.loose.mapped, st->u.loose.mapsize);
return -1;
}
/*****************************************************************
*
* Non-delta packed object stream
*
*****************************************************************/
static ssize_t read_istream_pack_non_delta(struct git_istream *st, char *buf,
size_t sz)
{
size_t total_read = 0;
switch (st->z_state) {
case z_unused:
memset(&st->z, 0, sizeof(st->z));
git_inflate_init(&st->z);
st->z_state = z_used;
break;
case z_done:
return 0;
case z_error:
return -1;
case z_used:
break;
}
while (total_read < sz) {
int status;
struct pack_window *window = NULL;
unsigned char *mapped;
mapped = use_pack(st->u.in_pack.pack, &window,
st->u.in_pack.pos, &st->z.avail_in);
st->z.next_out = (unsigned char *)buf + total_read;
st->z.avail_out = sz - total_read;
st->z.next_in = mapped;
status = git_inflate(&st->z, Z_FINISH);
st->u.in_pack.pos += st->z.next_in - mapped;
total_read = st->z.next_out - (unsigned char *)buf;
unuse_pack(&window);
if (status == Z_STREAM_END) {
git_inflate_end(&st->z);
st->z_state = z_done;
break;
}
/*
* Unlike the loose object case, we do not have to worry here
* about running out of input bytes and spinning infinitely. If
* we get Z_BUF_ERROR due to too few input bytes, then we'll
* replenish them in the next use_pack() call when we loop. If
* we truly hit the end of the pack (i.e., because it's corrupt
* or truncated), then use_pack() catches that and will die().
*/
if (status != Z_OK && status != Z_BUF_ERROR) {
git_inflate_end(&st->z);
st->z_state = z_error;
return -1;
}
}
return total_read;
}
static int close_istream_pack_non_delta(struct git_istream *st)
{
close_deflated_stream(st);
return 0;
}
static int open_istream_pack_non_delta(struct git_istream *st,
struct repository *r UNUSED,
const struct object_id *oid UNUSED,
enum object_type *type UNUSED)
{
struct pack_window *window;
enum object_type in_pack_type;
window = NULL;
in_pack_type = unpack_object_header(st->u.in_pack.pack,
&window,
&st->u.in_pack.pos,
&st->size);
unuse_pack(&window);
switch (in_pack_type) {
default:
return -1; /* we do not do deltas for now */
case OBJ_COMMIT:
case OBJ_TREE:
case OBJ_BLOB:
case OBJ_TAG:
break;
}
st->z_state = z_unused;
st->close = close_istream_pack_non_delta;
st->read = read_istream_pack_non_delta;
return 0;
}
/*****************************************************************
*
* In-core stream
*
*****************************************************************/
static int close_istream_incore(struct git_istream *st)
{
free(st->u.incore.buf);
return 0;
}
static ssize_t read_istream_incore(struct git_istream *st, char *buf, size_t sz)
{
size_t read_size = sz;
size_t remainder = st->size - st->u.incore.read_ptr;
if (remainder <= read_size)
read_size = remainder;
if (read_size) {
memcpy(buf, st->u.incore.buf + st->u.incore.read_ptr, read_size);
st->u.incore.read_ptr += read_size;
}
return read_size;
}
static int open_istream_incore(struct git_istream *st, struct repository *r,
const struct object_id *oid, enum object_type *type)
{
st->u.incore.buf = read_object_file_extended(r, oid, type, &st->size, 0);
st->u.incore.read_ptr = 0;
st->close = close_istream_incore;
st->read = read_istream_incore;
return st->u.incore.buf ? 0 : -1;
}
/*****************************************************************************
* static helpers variables and functions for users of streaming interface
*****************************************************************************/
static int istream_source(struct git_istream *st,
struct repository *r,
const struct object_id *oid,
enum object_type *type)
{
unsigned long size;
int status;
struct object_info oi = OBJECT_INFO_INIT;
oi.typep = type;
oi.sizep = &size;
status = oid_object_info_extended(r, oid, &oi, 0);
if (status < 0)
return status;
switch (oi.whence) {
case OI_LOOSE:
st->open = open_istream_loose;
return 0;
case OI_PACKED:
if (!oi.u.packed.is_delta && big_file_threshold < size) {
st->u.in_pack.pack = oi.u.packed.pack;
st->u.in_pack.pos = oi.u.packed.offset;
st->open = open_istream_pack_non_delta;
return 0;
}
/* fallthru */
default:
st->open = open_istream_incore;
return 0;
}
}
/****************************************************************
* Users of streaming interface
****************************************************************/
int close_istream(struct git_istream *st)
{
int r = st->close(st);
free(st);
return r;
}
ssize_t read_istream(struct git_istream *st, void *buf, size_t sz)
{
return st->read(st, buf, sz);
}
struct git_istream *open_istream(struct repository *r,
const struct object_id *oid,
enum object_type *type,
unsigned long *size,
struct stream_filter *filter)
{
struct git_istream *st = xmalloc(sizeof(*st));
const struct object_id *real = lookup_replace_object(r, oid);
int ret = istream_source(st, r, real, type);
if (ret) {
free(st);
return NULL;
}
if (st->open(st, r, real, type)) {
if (open_istream_incore(st, r, real, type)) {
free(st);
return NULL;
}
}
if (filter) {
/* Add "&& !is_null_stream_filter(filter)" for performance */
struct git_istream *nst = attach_stream_filter(st, filter);
if (!nst) {
close_istream(st);
return NULL;
}
st = nst;
}
*size = st->size;
return st;
}
int stream_blob_to_fd(int fd, const struct object_id *oid, struct stream_filter *filter,
int can_seek)
{
struct git_istream *st;
enum object_type type;
unsigned long sz;
ssize_t kept = 0;
int result = -1;
st = open_istream(the_repository, oid, &type, &sz, filter);
if (!st) {
if (filter)
free_stream_filter(filter);
return result;
}
if (type != OBJ_BLOB)
goto close_and_exit;
for (;;) {
char buf[1024 * 16];
ssize_t wrote, holeto;
ssize_t readlen = read_istream(st, buf, sizeof(buf));
if (readlen < 0)
goto close_and_exit;
if (!readlen)
break;
if (can_seek && sizeof(buf) == readlen) {
for (holeto = 0; holeto < readlen; holeto++)
if (buf[holeto])
break;
if (readlen == holeto) {
kept += holeto;
continue;
}
}
if (kept && lseek(fd, kept, SEEK_CUR) == (off_t) -1)
goto close_and_exit;
else
kept = 0;
wrote = write_in_full(fd, buf, readlen);
if (wrote < 0)
goto close_and_exit;
}
if (kept && (lseek(fd, kept - 1, SEEK_CUR) == (off_t) -1 ||
xwrite(fd, "", 1) != 1))
goto close_and_exit;
result = 0;
close_and_exit:
close_istream(st);
return result;
}
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