From 665d70ad033b115d8c14cdc2bcecf6c8b1947260 Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Mon, 17 Aug 2020 14:04:47 +0000 Subject: commit-graph: use the "hash version" byte The commit-graph format reserved a byte among the header of the file to store a "hash version". During the SHA-256 work, this was not modified because file formats are not necessarily intended to work across hash versions. If a repository has SHA-256 as its hash algorithm, it automatically up-shifts the lengths of object names in all necessary formats. However, since we have this byte available for adjusting the version, we can make the file formats more obviously incompatible instead of relying on other context from the repository. Update the oid_version() method in commit-graph.c to add a new value, 2, for sha-256. This automatically writes the new value in a SHA-256 repository _and_ verifies the value is correct. This is a breaking change relative to the current 'master' branch since 092b677 (Merge branch 'bc/sha-256-cvs-svn-updates', 2020-08-13) but it is not breaking relative to any released version of Git. The test impact is relatively minor: the output of 'test-tool read-graph' lists the header information, so those instances of '1' need to be replaced with a variable determined by GIT_TEST_DEFAULT_HASH. A more careful test is added that specifically creates a repository of each type then swaps the commit-graph files. The important value here is that the "git log" command succeeds while writing a message to stderr. Helped-by: brian m. carlson Signed-off-by: Derrick Stolee Reviewed-by: brian m. carlson Signed-off-by: Junio C Hamano --- Documentation/technical/commit-graph-format.txt | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'Documentation/technical') diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt index 440541045d..6ddbceba15 100644 --- a/Documentation/technical/commit-graph-format.txt +++ b/Documentation/technical/commit-graph-format.txt @@ -42,8 +42,13 @@ HEADER: 1-byte version number: Currently, the only valid version is 1. - 1-byte Hash Version (1 = SHA-1) - We infer the hash length (H) from this value. + 1-byte Hash Version + We infer the hash length (H) from this value: + 1 => SHA-1 + 2 => SHA-256 + If the hash type does not match the repository's hash algorithm, the + commit-graph file should be ignored with a warning presented to the + user. 1-byte number (C) of "chunks" -- cgit v1.3 From d96075428a9a1de720f6019242dadb5dbaa0ac16 Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Mon, 17 Aug 2020 14:04:48 +0000 Subject: multi-pack-index: use hash version byte Similar to the commit-graph format, the multi-pack-index format has a byte in the header intended to track the hash version used to write the file. This allows one to interpret the hash length without having the context of the repository config specifying the hash length. This was not modified as part of the SHA-256 work because the hash length was automatically up-shifted due to that config. Since we have this byte available, we can make the file formats more obviously incompatible instead of relying on other context from the repository. Add a new oid_version() method in midx.c similar to the one in commit-graph.c. This is specifically made separate from that implementation to avoid artificially linking the formats. The test impact requires a few more things than the corresponding change in the commit-graph format. Specifically, 'test-tool read-midx' was not writing anything about this header value to output. Since the value available in 'struct multi_pack_index' is hash_len instead of a version value, we output "20" or "32" instead of "1" or "2". Since we want a user to not have their Git commands fail if their multi-pack-index has the incorrect hash version compared to the repository's hash version, we relax the die() to an error() in load_multi_pack_index(). This has some effect on 'git multi-pack-index verify' as we need to check that a failed parse of a file that exists is actually a verify error. For that test that checks the hash version matches, we change the corrupted byte from "2" to "3" to ensure the test fails for both hash algorithms. Helped-by: brian m. carlson Signed-off-by: Derrick Stolee Reviewed-by: brian m. carlson Signed-off-by: Junio C Hamano --- Documentation/technical/pack-format.txt | 7 +++++- midx.c | 35 ++++++++++++++++++++++----- t/helper/test-read-midx.c | 8 ++++-- t/t5319-multi-pack-index.sh | 43 ++++++++++++++++++++++++++++++--- 4 files changed, 80 insertions(+), 13 deletions(-) (limited to 'Documentation/technical') diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index d3a142c652..16cf7e83aa 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -273,7 +273,12 @@ HEADER: Git only writes or recognizes version 1. 1-byte Object Id Version - Git only writes or recognizes version 1 (SHA1). + We infer the length of object IDs (OIDs) from this value: + 1 => SHA-1 + 2 => SHA-256 + If the hash type does not match the repository's hash algorithm, + the multi-pack-index file should be ignored with a warning + presented to the user. 1-byte number of "chunks" diff --git a/midx.c b/midx.c index a5fb797ede..551a30b907 100644 --- a/midx.c +++ b/midx.c @@ -17,7 +17,6 @@ #define MIDX_BYTE_HASH_VERSION 5 #define MIDX_BYTE_NUM_CHUNKS 6 #define MIDX_BYTE_NUM_PACKS 8 -#define MIDX_HASH_VERSION 1 #define MIDX_HEADER_SIZE 12 #define MIDX_MIN_SIZE (MIDX_HEADER_SIZE + the_hash_algo->rawsz) @@ -36,6 +35,18 @@ #define PACK_EXPIRED UINT_MAX +static uint8_t oid_version(void) +{ + switch (hash_algo_by_ptr(the_hash_algo)) { + case GIT_HASH_SHA1: + return 1; + case GIT_HASH_SHA256: + return 2; + default: + die(_("invalid hash version")); + } +} + static char *get_midx_filename(const char *object_dir) { return xstrfmt("%s/pack/multi-pack-index", object_dir); @@ -90,8 +101,11 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local m->version); hash_version = m->data[MIDX_BYTE_HASH_VERSION]; - if (hash_version != MIDX_HASH_VERSION) - die(_("hash version %u does not match"), hash_version); + if (hash_version != oid_version()) { + error(_("multi-pack-index hash version %u does not match version %u"), + hash_version, oid_version()); + goto cleanup_fail; + } m->hash_len = the_hash_algo->rawsz; m->num_chunks = m->data[MIDX_BYTE_NUM_CHUNKS]; @@ -418,7 +432,7 @@ static size_t write_midx_header(struct hashfile *f, hashwrite_be32(f, MIDX_SIGNATURE); byte_values[0] = MIDX_VERSION; - byte_values[1] = MIDX_HASH_VERSION; + byte_values[1] = oid_version(); byte_values[2] = num_chunks; byte_values[3] = 0; /* unused */ hashwrite(f, byte_values, sizeof(byte_values)); @@ -1105,8 +1119,17 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag struct multi_pack_index *m = load_multi_pack_index(object_dir, 1); verify_midx_error = 0; - if (!m) - return 0; + if (!m) { + int result = 0; + struct stat sb; + char *filename = get_midx_filename(object_dir); + if (!stat(filename, &sb)) { + error(_("multi-pack-index file exists, but failed to parse")); + result = 1; + } + free(filename); + return result; + } if (flags & MIDX_PROGRESS) progress = start_progress(_("Looking for referenced packfiles"), diff --git a/t/helper/test-read-midx.c b/t/helper/test-read-midx.c index 831b586d02..2430880f78 100644 --- a/t/helper/test-read-midx.c +++ b/t/helper/test-read-midx.c @@ -7,14 +7,18 @@ static int read_midx_file(const char *object_dir) { uint32_t i; - struct multi_pack_index *m = load_multi_pack_index(object_dir, 1); + struct multi_pack_index *m; + + setup_git_directory(); + m = load_multi_pack_index(object_dir, 1); if (!m) return 1; - printf("header: %08x %d %d %d\n", + printf("header: %08x %d %d %d %d\n", m->signature, m->version, + m->hash_len, m->num_chunks, m->num_packs); diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh index 7dfff0f8f4..09cbca4949 100755 --- a/t/t5319-multi-pack-index.sh +++ b/t/t5319-multi-pack-index.sh @@ -5,6 +5,8 @@ test_description='multi-pack-indexes' objdir=.git/objects +HASH_LEN=$(test_oid rawsz) + midx_read_expect () { NUM_PACKS=$1 NUM_OBJECTS=$2 @@ -13,7 +15,7 @@ midx_read_expect () { EXTRA_CHUNKS="$5" { cat <<-EOF && - header: 4d494458 1 $NUM_CHUNKS $NUM_PACKS + header: 4d494458 1 $HASH_LEN $NUM_CHUNKS $NUM_PACKS chunks: pack-names oid-fanout oid-lookup object-offsets$EXTRA_CHUNKS num_objects: $NUM_OBJECTS packs: @@ -46,7 +48,7 @@ test_expect_success "don't write midx with no packs" ' test_path_is_missing pack/multi-pack-index ' -test_expect_success "Warn if a midx contains no oid" ' +test_expect_success SHA1 'warn if a midx contains no oid' ' cp "$TEST_DIRECTORY"/t5319/no-objects.midx $objdir/pack/multi-pack-index && test_must_fail git multi-pack-index verify && rm $objdir/pack/multi-pack-index @@ -198,6 +200,40 @@ test_expect_success 'write midx with twelve packs' ' compare_results_with_midx "twelve packs" +test_expect_success 'warn on improper hash version' ' + git init --object-format=sha1 sha1 && + ( + cd sha1 && + git config core.multiPackIndex true && + test_commit 1 && + git repack -a && + git multi-pack-index write && + mv .git/objects/pack/multi-pack-index ../mpi-sha1 + ) && + git init --object-format=sha256 sha256 && + ( + cd sha256 && + git config core.multiPackIndex true && + test_commit 1 && + git repack -a && + git multi-pack-index write && + mv .git/objects/pack/multi-pack-index ../mpi-sha256 + ) && + ( + cd sha1 && + mv ../mpi-sha256 .git/objects/pack/multi-pack-index && + git log -1 2>err && + test_i18ngrep "multi-pack-index hash version 2 does not match version 1" err + ) && + ( + cd sha256 && + mv ../mpi-sha1 .git/objects/pack/multi-pack-index && + git log -1 2>err && + test_i18ngrep "multi-pack-index hash version 1 does not match version 2" err + ) +' + + test_expect_success 'verify multi-pack-index success' ' git multi-pack-index verify --object-dir=$objdir ' @@ -243,7 +279,6 @@ test_expect_success 'verify bad signature' ' "multi-pack-index signature" ' -HASH_LEN=$(test_oid rawsz) NUM_OBJECTS=74 MIDX_BYTE_VERSION=4 MIDX_BYTE_OID_VERSION=5 @@ -272,7 +307,7 @@ test_expect_success 'verify bad version' ' ' test_expect_success 'verify bad OID version' ' - corrupt_midx_and_verify $MIDX_BYTE_OID_VERSION "\02" $objdir \ + corrupt_midx_and_verify $MIDX_BYTE_OID_VERSION "\03" $objdir \ "hash version" ' -- cgit v1.3