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
reachable.c
#include "cache.h"
#include "refs.h"
#include "tag.h"
#include "commit.h"
#include "blob.h"
#include "diff.h"
#include "revision.h"
#include "reachable.h"
#include "cache-tree.h"
#include "progress.h"
#include "list-objects.h"
#include "packfile.h"
#include "worktree.h"
#include "object-store.h"
#include "pack-bitmap.h"
#include "pack-mtimes.h"
struct connectivity_progress {
struct progress *progress;
unsigned long count;
};
static void update_progress(struct connectivity_progress *cp)
{
cp->count++;
if ((cp->count & 1023) == 0)
display_progress(cp->progress, cp->count);
}
static int add_one_ref(const char *path, const struct object_id *oid,
int flag, void *cb_data)
{
struct rev_info *revs = (struct rev_info *)cb_data;
struct object *object;
if ((flag & REF_ISSYMREF) && (flag & REF_ISBROKEN)) {
warning("symbolic ref is dangling: %s", path);
return 0;
}
object = parse_object_or_die(oid, path);
add_pending_object(revs, object, "");
return 0;
}
/*
* The traversal will have already marked us as SEEN, so we
* only need to handle any progress reporting here.
*/
static void mark_object(struct object *obj, const char *name, void *data)
{
update_progress(data);
}
static void mark_commit(struct commit *c, void *data)
{
mark_object(&c->object, NULL, data);
}
struct recent_data {
struct rev_info *revs;
timestamp_t timestamp;
report_recent_object_fn *cb;
int ignore_in_core_kept_packs;
};
static void add_recent_object(const struct object_id *oid,
struct packed_git *pack,
off_t offset,
timestamp_t mtime,
struct recent_data *data)
{
struct object *obj;
enum object_type type;
if (mtime <= data->timestamp)
return;
/*
* We do not want to call parse_object here, because
* inflating blobs and trees could be very expensive.
* However, we do need to know the correct type for
* later processing, and the revision machinery expects
* commits and tags to have been parsed.
*/
type = oid_object_info(the_repository, oid, NULL);
if (type < 0)
die("unable to get object info for %s", oid_to_hex(oid));
switch (type) {
case OBJ_TAG:
case OBJ_COMMIT:
obj = parse_object_or_die(oid, NULL);
break;
case OBJ_TREE:
obj = (struct object *)lookup_tree(the_repository, oid);
break;
case OBJ_BLOB:
obj = (struct object *)lookup_blob(the_repository, oid);
break;
default:
die("unknown object type for %s: %s",
oid_to_hex(oid), type_name(type));
}
if (!obj)
die("unable to lookup %s", oid_to_hex(oid));
add_pending_object(data->revs, obj, "");
if (data->cb)
data->cb(obj, pack, offset, mtime);
}
static int want_recent_object(struct recent_data *data,
const struct object_id *oid)
{
if (data->ignore_in_core_kept_packs &&
has_object_kept_pack(oid, IN_CORE_KEEP_PACKS))
return 0;
return 1;
}
static int add_recent_loose(const struct object_id *oid,
const char *path, void *data)
{
struct stat st;
struct object *obj;
if (!want_recent_object(data, oid))
return 0;
obj = lookup_object(the_repository, oid);
if (obj && obj->flags & SEEN)
return 0;
if (stat(path, &st) < 0) {
/*
* It's OK if an object went away during our iteration; this
* could be due to a simultaneous repack. But anything else
* we should abort, since we might then fail to mark objects
* which should not be pruned.
*/
if (errno == ENOENT)
return 0;
return error_errno("unable to stat %s", oid_to_hex(oid));
}
add_recent_object(oid, NULL, 0, st.st_mtime, data);
return 0;
}
static int add_recent_packed(const struct object_id *oid,
struct packed_git *p, uint32_t pos,
void *data)
{
struct object *obj;
timestamp_t mtime = p->mtime;
if (!want_recent_object(data, oid))
return 0;
obj = lookup_object(the_repository, oid);
if (obj && obj->flags & SEEN)
return 0;
if (p->is_cruft) {
if (load_pack_mtimes(p) < 0)
die(_("could not load cruft pack .mtimes"));
mtime = nth_packed_mtime(p, pos);
}
add_recent_object(oid, p, nth_packed_object_offset(p, pos), mtime, data);
return 0;
}
int add_unseen_recent_objects_to_traversal(struct rev_info *revs,
timestamp_t timestamp,
report_recent_object_fn *cb,
int ignore_in_core_kept_packs)
{
struct recent_data data;
enum for_each_object_flags flags;
int r;
data.revs = revs;
data.timestamp = timestamp;
data.cb = cb;
data.ignore_in_core_kept_packs = ignore_in_core_kept_packs;
r = for_each_loose_object(add_recent_loose, &data,
FOR_EACH_OBJECT_LOCAL_ONLY);
if (r)
return r;
flags = FOR_EACH_OBJECT_LOCAL_ONLY | FOR_EACH_OBJECT_PACK_ORDER;
if (ignore_in_core_kept_packs)
flags |= FOR_EACH_OBJECT_SKIP_IN_CORE_KEPT_PACKS;
return for_each_packed_object(add_recent_packed, &data, flags);
}
static int mark_object_seen(const struct object_id *oid,
enum object_type type,
int exclude,
uint32_t name_hash,
struct packed_git *found_pack,
off_t found_offset)
{
struct object *obj = lookup_object_by_type(the_repository, oid, type);
if (!obj)
die("unable to create object '%s'", oid_to_hex(oid));
obj->flags |= SEEN;
return 0;
}
void mark_reachable_objects(struct rev_info *revs, int mark_reflog,
timestamp_t mark_recent, struct progress *progress)
{
struct connectivity_progress cp;
struct bitmap_index *bitmap_git;
/*
* Set up revision parsing, and mark us as being interested
* in all object types, not just commits.
*/
revs->tag_objects = 1;
revs->blob_objects = 1;
revs->tree_objects = 1;
/* Add all refs from the index file */
add_index_objects_to_pending(revs, 0);
/* Add all external refs */
for_each_ref(add_one_ref, revs);
/* detached HEAD is not included in the list above */
head_ref(add_one_ref, revs);
other_head_refs(add_one_ref, revs);
/* Add all reflog info */
if (mark_reflog)
add_reflogs_to_pending(revs, 0);
cp.progress = progress;
cp.count = 0;
bitmap_git = prepare_bitmap_walk(revs, 0);
if (bitmap_git) {
traverse_bitmap_commit_list(bitmap_git, revs, mark_object_seen);
free_bitmap_index(bitmap_git);
} else {
if (prepare_revision_walk(revs))
die("revision walk setup failed");
traverse_commit_list(revs, mark_commit, mark_object, &cp);
}
if (mark_recent) {
revs->ignore_missing_links = 1;
if (add_unseen_recent_objects_to_traversal(revs, mark_recent,
NULL, 0))
die("unable to mark recent objects");
if (prepare_revision_walk(revs))
die("revision walk setup failed");
traverse_commit_list(revs, mark_commit, mark_object, &cp);
}
display_progress(cp.progress, cp.count);
}
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