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index-pack, unpack-objects: use get_be32() for reading pack header

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Both of these commands read the incoming pack into a static unsigned
char buffer in BSS, and then parse it by casting the start of the buffer
to a struct pack_header. This can result in SIGBUS on some platforms if
the compiler doesn't place the buffer in a position that is properly
aligned for 4-byte integers.

This reportedly happens with unpack-objects (but not index-pack) on
sparc64 when compiled with clang (but not gcc). But we are definitely in
the wrong in both spots; since the buffer's type is unsigned char, we
can't depend on larger alignment. When it works it is only because we
are lucky.

We'll fix this by switching to get_be32() to read the headers (just like
the last few commits similarly switched us to put_be32() for writing
into the same buffer).

It would be nice to factor this out into a common helper function, but
the interface ends up quite awkward. Either the caller needs to hardcode
how many bytes we'll need, or it needs to pass us its fill()/use()
functions as pointers. So I've just fixed both spots in the same way;
this is not code that is likely to be repeated a third time (most of the
pack reading code uses an mmap'd buffer, which should be properly
aligned).

I did make one tweak to the shared code: our pack_version_ok() macro
expects us to pass the big-endian value we'd get by casting. We can
introduce a "native" variant which uses the host integer ordering.

Reported-by: Koakuma <koachan@protonmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King
2025-01-19 08:25:47 -05:00
committed by Junio C Hamano
parent 4f02f4d68d
commit f1299bff26
3 changed files with 16 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
builtin/index-pack.c
View File

@ -363,16 +363,18 @@ static const char *open_pack_file(const char *pack_name)
static void parse_pack_header(void)
{
struct pack_header *hdr = fill(sizeof(struct pack_header));
unsigned char *hdr = fill(sizeof(struct pack_header));
/* Header consistency check */
if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
if (get_be32(hdr) != PACK_SIGNATURE)
die(_("pack signature mismatch"));
if (!pack_version_ok(hdr->hdr_version))
hdr += 4;
if (!pack_version_ok_native(get_be32(hdr)))
die(_("pack version %"PRIu32" unsupported"),
ntohl(hdr->hdr_version));
get_be32(hdr));
hdr += 4;
nr_objects = ntohl(hdr->hdr_entries);
nr_objects = get_be32(hdr);
use(sizeof(struct pack_header));
}

13
builtin/unpack-objects.c
View File

@ -576,15 +576,16 @@ static void unpack_one(unsigned nr)
static void unpack_all(void)
{
int i;
struct pack_header *hdr = fill(sizeof(struct pack_header));
unsigned char *hdr = fill(sizeof(struct pack_header));
nr_objects = ntohl(hdr->hdr_entries);
if (ntohl(hdr->hdr_signature) != PACK_SIGNATURE)
if (get_be32(hdr) != PACK_SIGNATURE)
die("bad pack file");
if (!pack_version_ok(hdr->hdr_version))
hdr += 4;
if (!pack_version_ok_native(get_be32(hdr)))
die("unknown pack file version %"PRIu32,
ntohl(hdr->hdr_version));
get_be32(hdr));
hdr += 4;
nr_objects = get_be32(hdr);
use(sizeof(struct pack_header));
if (!quiet)

3
pack.h
View File

@ -13,7 +13,8 @@ struct repository;
*/
#define PACK_SIGNATURE 0x5041434b /* "PACK" */
#define PACK_VERSION 2
#define pack_version_ok(v) ((v) == htonl(2) || (v) == htonl(3))
#define pack_version_ok(v) pack_version_ok_native(ntohl(v))
#define pack_version_ok_native(v) ((v) == 2 || (v) == 3)
struct pack_header {
uint32_t hdr_signature;
uint32_t hdr_version;