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>
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pack-bitmap.h
#ifndef PACK_BITMAP_H
#define PACK_BITMAP_H
#include "ewah/ewok.h"
#include "khash.h"
#include "pack.h"
#include "pack-objects.h"
#include "string-list.h"
struct commit;
struct repository;
struct rev_info;
static const char BITMAP_IDX_SIGNATURE[] = {'B', 'I', 'T', 'M'};
struct bitmap_disk_header {
char magic[ARRAY_SIZE(BITMAP_IDX_SIGNATURE)];
uint16_t version;
uint16_t options;
uint32_t entry_count;
unsigned char checksum[GIT_MAX_RAWSZ];
};
#define NEEDS_BITMAP (1u<<22)
/*
* The width in bytes of a single triplet in the lookup table
* extension:
* (commit_pos, offset, xor_row)
*
* whose fields ar 32-, 64-, 32- bits wide, respectively.
*/
#define BITMAP_LOOKUP_TABLE_TRIPLET_WIDTH (16)
enum pack_bitmap_opts {
BITMAP_OPT_FULL_DAG = 0x1,
BITMAP_OPT_HASH_CACHE = 0x4,
BITMAP_OPT_LOOKUP_TABLE = 0x10,
};
enum pack_bitmap_flags {
BITMAP_FLAG_REUSE = 0x1
};
typedef int (*show_reachable_fn)(
const struct object_id *oid,
enum object_type type,
int flags,
uint32_t hash,
struct packed_git *found_pack,
off_t found_offset);
struct bitmap_index;
struct bitmap_index *prepare_bitmap_git(struct repository *r);
struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx);
void count_bitmap_commit_list(struct bitmap_index *, uint32_t *commits,
uint32_t *trees, uint32_t *blobs, uint32_t *tags);
void traverse_bitmap_commit_list(struct bitmap_index *,
struct rev_info *revs,
show_reachable_fn show_reachable);
void test_bitmap_walk(struct rev_info *revs);
int test_bitmap_commits(struct repository *r);
int test_bitmap_hashes(struct repository *r);
struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs,
int filter_provided_objects);
uint32_t midx_preferred_pack(struct bitmap_index *bitmap_git);
int reuse_partial_packfile_from_bitmap(struct bitmap_index *,
struct packed_git **packfile,
uint32_t *entries,
struct bitmap **reuse_out);
int rebuild_existing_bitmaps(struct bitmap_index *, struct packing_data *mapping,
kh_oid_map_t *reused_bitmaps, int show_progress);
void free_bitmap_index(struct bitmap_index *);
int bitmap_walk_contains(struct bitmap_index *,
struct bitmap *bitmap, const struct object_id *oid);
/*
* After a traversal has been performed by prepare_bitmap_walk(), this can be
* queried to see if a particular object was reachable from any of the
* objects flagged as UNINTERESTING.
*/
int bitmap_has_oid_in_uninteresting(struct bitmap_index *, const struct object_id *oid);
off_t get_disk_usage_from_bitmap(struct bitmap_index *, struct rev_info *);
void bitmap_writer_show_progress(int show);
void bitmap_writer_set_checksum(const unsigned char *sha1);
void bitmap_writer_build_type_index(struct packing_data *to_pack,
struct pack_idx_entry **index,
uint32_t index_nr);
uint32_t *create_bitmap_mapping(struct bitmap_index *bitmap_git,
struct packing_data *mapping);
int rebuild_bitmap(const uint32_t *reposition,
struct ewah_bitmap *source,
struct bitmap *dest);
struct ewah_bitmap *bitmap_for_commit(struct bitmap_index *bitmap_git,
struct commit *commit);
void bitmap_writer_select_commits(struct commit **indexed_commits,
unsigned int indexed_commits_nr, int max_bitmaps);
int bitmap_writer_build(struct packing_data *to_pack);
void bitmap_writer_finish(struct pack_idx_entry **index,
uint32_t index_nr,
const char *filename,
uint16_t options);
char *midx_bitmap_filename(struct multi_pack_index *midx);
char *pack_bitmap_filename(struct packed_git *p);
int bitmap_is_midx(struct bitmap_index *bitmap_git);
const struct string_list *bitmap_preferred_tips(struct repository *r);
int bitmap_is_preferred_refname(struct repository *r, const char *refname);
#endif
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