Subject: Re: [PATCH v2 03/11] odb, packfile: use size_t for streaming object sizes

From: Torsten Bögershausen <[email-masked]>
Date: Tue, 5 May 2026 21:27:22 +0200

On Mon, May 04, 2026 at 05:08:20PM +0000, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <[email-masked]>
> 
> The odb_read_stream structure uses unsigned long for the size field,
> which is 32-bit on Windows even in 64-bit builds. When streaming
> objects larger than 4GB, the size would be truncated to zero or an
> incorrect value, resulting in empty files being written to disk.
> 
> Change the size field in odb_read_stream to size_t and introduce
> unpack_object_header_sz() to return sizes via size_t pointer. Since
> object_info.sizep remains unsigned long for API compatibility, use
> temporary variables where the types differ, with comments noting the
> truncation limitation for code paths that still use unsigned long.
> 
> This was originally authored by LordKiRon <https://github.com/LordKiRon>,
> who preferred not to reveal their real name and therefore agreed that I
> take over authorship.
> 
> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  builtin/pack-objects.c       | 23 ++++++++++++++++-------
>  object-file.c                | 10 +++++++++-
>  odb/streaming.c              | 13 ++++++++++++-
>  odb/streaming.h              |  2 +-
>  oss-fuzz/fuzz-pack-headers.c |  2 +-
>  pack-bitmap.c                |  2 +-
>  pack-check.c                 |  6 ++++--
>  packfile.c                   | 24 +++++++++++++++---------
>  packfile.h                   |  4 ++--
>  9 files changed, 61 insertions(+), 25 deletions(-)
> 

> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index dd2480a73d..aa4b1cb9b8 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c

I haven't been able to follow all changes, so this may be false alarm.
Do we need a cast_size_t_to_ulong() somewhere ?

> @@ -629,14 +629,21 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
>  	struct packed_git *p = IN_PACK(entry);
>  	struct pack_window *w_curs = NULL;
>  	uint32_t pos;
> -	off_t offset;
> +	off_t offset, cur;
>  	enum object_type type = oe_type(entry);
> +	enum object_type in_pack_type;
>  	off_t datalen;
>  	unsigned char header[MAX_PACK_OBJECT_HEADER],
>  		      dheader[MAX_PACK_OBJECT_HEADER];
>  	unsigned hdrlen;
>  	const unsigned hashsz = the_hash_algo->rawsz;
> -	unsigned long entry_size = SIZE(entry);
> +	size_t entry_size;
> +
> +	cur = entry->in_pack_offset;
> +	in_pack_type = unpack_object_header(p, &w_curs, &cur, &entry_size);
> +	if (in_pack_type < 0)
> +		die(_("write_reuse_object: unable to parse object header of %s"),
> +		    oid_to_hex(&entry->idx.oid));
>  
>  	if (DELTA(entry))
>  		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
> @@ -1087,7 +1094,7 @@ static void write_reused_pack_one(struct packed_git *reuse_packfile,
>  {
>  	off_t offset, next, cur;
>  	enum object_type type;
> -	unsigned long size;
> +	size_t size;
>  
>  	offset = pack_pos_to_offset(reuse_packfile, pos);
>  	next = pack_pos_to_offset(reuse_packfile, pos + 1);
> @@ -2243,7 +2250,7 @@ static void check_object(struct object_entry *entry, uint32_t object_index)
>  		off_t ofs;
>  		unsigned char *buf, c;
>  		enum object_type type;
> -		unsigned long in_pack_size;
> +		size_t in_pack_size;
>  
>  		buf = use_pack(p, &w_curs, entry->in_pack_offset, &avail);
>  
> @@ -2734,16 +2741,18 @@ unsigned long oe_get_size_slow(struct packing_data *pack,
>  	struct pack_window *w_curs;
>  	unsigned char *buf;
>  	enum object_type type;
> -	unsigned long used, avail, size;
> +	unsigned long used, avail;
> +	size_t size;
>  
>  	if (e->type_ != OBJ_OFS_DELTA && e->type_ != OBJ_REF_DELTA) {
> +		unsigned long sz;
>  		packing_data_lock(&to_pack);
>  		if (odb_read_object_info(the_repository->objects,
> -					 &e->idx.oid, &size) < 0)
> +					 &e->idx.oid, &sz) < 0)
>  			die(_("unable to get size of %s"),
>  			    oid_to_hex(&e->idx.oid));
>  		packing_data_unlock(&to_pack);
> -		return size;
> +		return sz;
>  	}
>  
>  	p = oe_in_pack(pack, e);
> diff --git a/object-file.c b/object-file.c
> index 086b2b65ff..0be2981c7a 100644
> --- a/object-file.c
> +++ b/object-file.c
> @@ -2326,6 +2326,7 @@ int odb_source_loose_read_object_stream(struct odb_read_stream **out,
>  	struct object_info oi = OBJECT_INFO_INIT;
>  	struct odb_loose_read_stream *st;
>  	unsigned long mapsize;
> +	unsigned long size_ul;
>  	void *mapped;
>  
>  	mapped = odb_source_loose_map_object(source, oid, &mapsize);
> @@ -2349,11 +2350,18 @@ int odb_source_loose_read_object_stream(struct odb_read_stream **out,
>  		goto error;
>  	}
>  
> -	oi.sizep = &st->base.size;
> +	/*
> +	 * object_info.sizep is unsigned long* (32-bit on Windows), but
> +	 * st->base.size is size_t (64-bit). Use temporary variable.
> +	 * Note: loose objects >4GB would still truncate here, but such
> +	 * large loose objects are uncommon (they'd normally be packed).
> +	 */
> +	oi.sizep = &size_ul;
>  	oi.typep = &st->base.type;
>  
>  	if (parse_loose_header(st->hdr, &oi) < 0 || st->base.type < 0)
>  		goto error;
> +	st->base.size = size_ul;
>  
>  	st->mapped = mapped;
>  	st->mapsize = mapsize;
> diff --git a/odb/streaming.c b/odb/streaming.c
> index 5927a12954..af2adf5ce7 100644
> --- a/odb/streaming.c
> +++ b/odb/streaming.c
> @@ -157,15 +157,26 @@ static int open_istream_incore(struct odb_read_stream **out,
>  		.base.read = read_istream_incore,
>  	};
>  	struct odb_incore_read_stream *st;
> +	unsigned long size_ul;
>  	int ret;
>  
>  	oi.typep = &stream.base.type;
> -	oi.sizep = &stream.base.size;
> +	/*
> +	 * object_info.sizep is unsigned long* (32-bit on Windows), but
> +	 * stream.base.size is size_t (64-bit). We use a temporary variable
> +	 * because the types are incompatible. Note: this path still truncates
> +	 * for >4GB objects, but large objects should use pack streaming
> +	 * (packfile_store_read_object_stream) which handles size_t properly.
> +	 * This incore fallback is only used for small objects or when pack
> +	 * streaming is unavailable.
> +	 */
> +	oi.sizep = &size_ul;
>  	oi.contentp = (void **)&stream.buf;
>  	ret = odb_read_object_info_extended(odb, oid, &oi,
>  					    OBJECT_INFO_DIE_IF_CORRUPT);
>  	if (ret)
>  		return ret;
> +	stream.base.size = size_ul;
>  
>  	CALLOC_ARRAY(st, 1);
>  	*st = stream;
> diff --git a/odb/streaming.h b/odb/streaming.h
> index c7861f7e13..517e2ea2d3 100644
> --- a/odb/streaming.h
> +++ b/odb/streaming.h
> @@ -21,7 +21,7 @@ struct odb_read_stream {
>  	odb_read_stream_close_fn close;
>  	odb_read_stream_read_fn read;
>  	enum object_type type;
> -	unsigned long size; /* inflated size of full object */
> +	size_t size; /* inflated size of full object */
>  };
>  
>  /*
> diff --git a/oss-fuzz/fuzz-pack-headers.c b/oss-fuzz/fuzz-pack-headers.c
> index 150c0f5fa2..ef61ab577c 100644
> --- a/oss-fuzz/fuzz-pack-headers.c
> +++ b/oss-fuzz/fuzz-pack-headers.c
> @@ -6,7 +6,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
>  int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
>  {
>  	enum object_type type;
> -	unsigned long len;
> +	size_t len;
>  
>  	unpack_object_header_buffer((const unsigned char *)data,
>  				    (unsigned long)size, &type, &len);
> diff --git a/pack-bitmap.c b/pack-bitmap.c
> index f6ec18d83a..f9af8a96bd 100644
> --- a/pack-bitmap.c
> +++ b/pack-bitmap.c
> @@ -2270,7 +2270,7 @@ static int try_partial_reuse(struct bitmap_index *bitmap_git,
>  {
>  	off_t delta_obj_offset;
>  	enum object_type type;
> -	unsigned long size;
> +	size_t size;
>  
>  	if (pack_pos >= pack->p->num_objects)
>  		return -1; /* not actually in the pack */
> diff --git a/pack-check.c b/pack-check.c
> index 79992bb509..2792f34d25 100644
> --- a/pack-check.c
> +++ b/pack-check.c
> @@ -110,7 +110,7 @@ static int verify_packfile(struct repository *r,
>  		void *data;
>  		struct object_id oid;
>  		enum object_type type;
> -		unsigned long size;
> +		size_t size;
>  		off_t curpos;
>  		int data_valid;
>  
> @@ -143,7 +143,9 @@ static int verify_packfile(struct repository *r,
>  			data = NULL;
>  			data_valid = 0;
>  		} else {
> -			data = unpack_entry(r, p, entries[i].offset, &type, &size);
> +			unsigned long sz;
> +			data = unpack_entry(r, p, entries[i].offset, &type, &sz);
> +			size = sz;
>  			data_valid = 1;
>  		}
>  
> diff --git a/packfile.c b/packfile.c
> index b012d648ad..fdae91dd11 100644
> --- a/packfile.c
> +++ b/packfile.c
> @@ -1133,7 +1133,7 @@ out:
>  }
>  
>  unsigned long unpack_object_header_buffer(const unsigned char *buf,
> -		unsigned long len, enum object_type *type, unsigned long *sizep)
> +		unsigned long len, enum object_type *type, size_t *sizep)
>  {
>  	unsigned shift;
>  	size_t size, c;
> @@ -1144,7 +1144,11 @@ unsigned long unpack_object_header_buffer(const unsigned char *buf,
>  	size = c & 15;
>  	shift = 4;
>  	while (c & 0x80) {
> -		if (len <= used || (bitsizeof(long) - 7) < shift) {
> +		/*
> +		 * Each continuation byte adds 7 bits. Ensure shift won't
> +		 * overflow size_t (use size_t not long for 64-bit on Windows).
> +		 */
> +		if (len <= used || (bitsizeof(size_t) - 7) < shift) {
>  			error("bad object header");
>  			size = used = 0;
>  			break;
> @@ -1153,7 +1157,7 @@ unsigned long unpack_object_header_buffer(const unsigned char *buf,
>  		size = st_add(size, st_left_shift(c & 0x7f, shift));
>  		shift += 7;
>  	}
> -	*sizep = cast_size_t_to_ulong(size);
> +	*sizep = size;
>  	return used;
>  }
>  
> @@ -1215,7 +1219,7 @@ unsigned long get_size_from_delta(struct packed_git *p,
>  int unpack_object_header(struct packed_git *p,
>  			 struct pack_window **w_curs,
>  			 off_t *curpos,
> -			 unsigned long *sizep)
> +			 size_t *sizep)
>  {
>  	unsigned char *base;
>  	unsigned long left;
> @@ -1367,7 +1371,7 @@ static enum object_type packed_to_object_type(struct repository *r,
>  
>  	while (type == OBJ_OFS_DELTA || type == OBJ_REF_DELTA) {
>  		off_t base_offset;
> -		unsigned long size;
> +		size_t size;
>  		/* Push the object we're going to leave behind */
>  		if (poi_stack_nr >= poi_stack_alloc && poi_stack == small_poi_stack) {
>  			poi_stack_alloc = alloc_nr(poi_stack_nr);
> @@ -1586,7 +1590,7 @@ static int packed_object_info_with_index_pos(struct packed_git *p, off_t obj_off
>  					     uint32_t *maybe_index_pos, struct object_info *oi)
>  {
>  	struct pack_window *w_curs = NULL;
> -	unsigned long size;
> +	size_t size;
>  	off_t curpos = obj_offset;
>  	enum object_type type = OBJ_NONE;
>  	uint32_t pack_pos;
> @@ -1778,7 +1782,7 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
>  	struct pack_window *w_curs = NULL;
>  	off_t curpos = obj_offset;
>  	void *data = NULL;
> -	unsigned long size;
> +	size_t size;
>  	enum object_type type;
>  	struct unpack_entry_stack_ent small_delta_stack[UNPACK_ENTRY_STACK_PREALLOC];
>  	struct unpack_entry_stack_ent *delta_stack = small_delta_stack;
> @@ -1943,8 +1947,10 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
>  			      (uintmax_t)curpos, p->pack_name);
>  			data = NULL;
>  		} else {
> +			unsigned long sz;
>  			data = patch_delta(base, base_size, delta_data,
> -					   delta_size, &size);
> +					   delta_size, &sz);
> +			size = sz;
>  
>  			/*
>  			 * We could not apply the delta; warn the user, but
> @@ -2929,7 +2935,7 @@ int packfile_read_object_stream(struct odb_read_stream **out,
>  	struct odb_packed_read_stream *stream;
>  	struct pack_window *window = NULL;
>  	enum object_type in_pack_type;
> -	unsigned long size;
> +	size_t size;
>  
>  	in_pack_type = unpack_object_header(pack, &window, &offset, &size);
>  	unuse_pack(&window);
> diff --git a/packfile.h b/packfile.h
> index 9b647da7dd..49d6bdecf6 100644
> --- a/packfile.h
> +++ b/packfile.h
> @@ -456,9 +456,9 @@ off_t find_pack_entry_one(const struct object_id *oid, struct packed_git *);
>  
>  int is_pack_valid(struct packed_git *);
>  void *unpack_entry(struct repository *r, struct packed_git *, off_t, enum object_type *, unsigned long *);
> -unsigned long unpack_object_header_buffer(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep);
> +unsigned long unpack_object_header_buffer(const unsigned char *buf, unsigned long len, enum object_type *type, size_t *sizep);
>  unsigned long get_size_from_delta(struct packed_git *, struct pack_window **, off_t);
> -int unpack_object_header(struct packed_git *, struct pack_window **, off_t *, unsigned long *);
> +int unpack_object_header(struct packed_git *, struct pack_window **, off_t *, size_t *);
>  off_t get_delta_base(struct packed_git *p, struct pack_window **w_curs,
>  		     off_t *curpos, enum object_type type,
>  		     off_t delta_obj_offset);
> -- 
> gitgitgadget
> 
>