[PATCH v2 4/5] index-pack, unpack-objects: use get_be32() for reading pack header
- From
Jeff King <peff@peff.net>
- Date
- Jan 19, 2025, 13:25 UTC
- Message-ID
- <20250119132547.GD1552263@coredump.intra.peff.net>
- In-Reply-To
- <20250119131224.GA1541095@coredump.intra.peff.net>
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> --- New in v2.
I did write the function-pointer version, and it's not even _too_ bad to read. But while trying to write a comment documenting the helper, it was just too gross to justify.
builtin/index-pack.c | 12 +++++++----- builtin/unpack-objects.c | 13 +++++++------ pack.h | 3 ++- 3 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/builtin/index-pack.c b/builtin/index-pack.c index 75b84f78f4..d6fd4bbde6 100644 --- a/builtin/index-pack.c +++ b/builtin/index-pack.c @@ -379,16 +379,18 @@ 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)); } diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c index cf2bc5c531..76c6a9031b 100644 --- a/builtin/unpack-objects.c +++ b/builtin/unpack-objects.c @@ -579,15 +579,16 @@ 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) diff --git a/pack.h b/pack.h index a8da040629..78f8d8b213 100644 --- a/pack.h +++ b/pack.h @@ -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;
-- 2.48.1.466.g22b8cfd1fa