[PATCH v4 6/8] hash.h: scaffolding for _unsafe hashing variants
- From
Taylor Blau <me@ttaylorr.com>
- Date
- Sep 24, 2024, 17:32 UTC
- Message-ID
- <d300e9c68879faf837c65455e39b4aa07c1e1b03.1727199118.git.me@ttaylorr.com>
- In-Reply-To
- <cover.1727199118.git.me@ttaylorr.com>
Git's default SHA-1 implementation is collision-detecting, which hardens us against known SHA-1 attacks against Git objects. This makes Git object writes safer at the expense of some speed when hashing through the collision-detecting implementation, which is slower than non-collision detecting alternatives.
Prepare for loading a separate "unsafe" SHA-1 implementation that can be used for non-cryptographic purposes, like computing the checksum of files that use the hashwrite() API.
This commit does not actually introduce any new compile-time knobs to control which implementation is used as the unsafe SHA-1 variant, but does add scaffolding so that the "git_hash_algo" structure has five new function pointers which are "unsafe" variants of the five existing hashing-related function pointers:
- git_hash_init_fn unsafe_init_fn - git_hash_clone_fn unsafe_clone_fn - git_hash_update_fn unsafe_update_fn - git_hash_final_fn unsafe_final_fn - git_hash_final_oid_fn unsafe_final_oid_fn
The following commit will introduce compile-time knobs to specify which SHA-1 implementation is used for non-cryptographic uses.
Signed-off-by: Taylor Blau <me@ttaylorr.com> --- hash.h | 42 ++++++++++++++++++++++++++++++++++++++++++ object-file.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+)
diff --git a/hash.h b/hash.h index 72ffbc862e5..96458b129f9 100644 --- a/hash.h +++ b/hash.h @@ -44,14 +44,32 @@ #define platform_SHA1_Final SHA1_Final #endif +#ifndef platform_SHA_CTX_unsafe +# define platform_SHA_CTX_unsafe platform_SHA_CTX +# define platform_SHA1_Init_unsafe platform_SHA1_Init +# define platform_SHA1_Update_unsafe platform_SHA1_Update +# define platform_SHA1_Final_unsafe platform_SHA1_Final +# ifdef platform_SHA1_Clone +# define platform_SHA1_Clone_unsafe platform_SHA1_Clone +# endif +#endif + #define git_SHA_CTX platform_SHA_CTX #define git_SHA1_Init platform_SHA1_Init #define git_SHA1_Update platform_SHA1_Update #define git_SHA1_Final platform_SHA1_Final +#define git_SHA_CTX_unsafe platform_SHA_CTX_unsafe +#define git_SHA1_Init_unsafe platform_SHA1_Init_unsafe +#define git_SHA1_Update_unsafe platform_SHA1_Update_unsafe +#define git_SHA1_Final_unsafe platform_SHA1_Final_unsafe + #ifdef platform_SHA1_Clone #define git_SHA1_Clone platform_SHA1_Clone #endif +#ifdef platform_SHA1_Clone_unsafe +# define git_SHA1_Clone_unsafe platform_SHA1_Clone_unsafe +#endif #ifndef platform_SHA256_CTX #define platform_SHA256_CTX SHA256_CTX @@ -81,6 +99,13 @@ static inline void git_SHA1_Clone(git_SHA_CTX *dst, const git_SHA_CTX *src) memcpy(dst, src, sizeof(*dst)); } #endif +#ifndef SHA1_NEEDS_CLONE_HELPER_UNSAFE +static inline void git_SHA1_Clone_unsafe(git_SHA_CTX_unsafe *dst, + const git_SHA_CTX_unsafe *src) +{ + memcpy(dst, src, sizeof(*dst)); +} +#endif #ifndef SHA256_NEEDS_CLONE_HELPER static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *src) @@ -178,6 +203,8 @@ enum get_oid_result { /* A suitably aligned type for stack allocations of hash contexts. */ union git_hash_ctx { git_SHA_CTX sha1; + git_SHA_CTX_unsafe sha1_unsafe; + git_SHA256_CTX sha256; }; typedef union git_hash_ctx git_hash_ctx; @@ -222,6 +249,21 @@ struct git_hash_algo { /* The hash finalization function for object IDs. */ git_hash_final_oid_fn final_oid_fn; + /* The non-cryptographic hash initialization function. */ + git_hash_init_fn unsafe_init_fn; + + /* The non-cryptographic hash context cloning function. */ + git_hash_clone_fn unsafe_clone_fn; + + /* The non-cryptographic hash update function. */ + git_hash_update_fn unsafe_update_fn; + + /* The non-cryptographic hash finalization function. */ + git_hash_final_fn unsafe_final_fn; + + /* The non-cryptographic hash finalization function. */ + git_hash_final_oid_fn unsafe_final_oid_fn; + /* The OID of the empty tree. */ const struct object_id *empty_tree; diff --git a/object-file.c b/object-file.c index b9a3a1f62db..196c9e2df8b 100644 --- a/object-file.c +++ b/object-file.c @@ -115,6 +115,33 @@ static void git_hash_sha1_final_oid(struct object_id *oid, git_hash_ctx *ctx) oid->algo = GIT_HASH_SHA1; } +static void git_hash_sha1_init_unsafe(git_hash_ctx *ctx) +{ + git_SHA1_Init_unsafe(&ctx->sha1_unsafe); +} + +static void git_hash_sha1_clone_unsafe(git_hash_ctx *dst, const git_hash_ctx *src) +{ + git_SHA1_Clone_unsafe(&dst->sha1_unsafe, &src->sha1_unsafe); +} + +static void git_hash_sha1_update_unsafe(git_hash_ctx *ctx, const void *data, + size_t len) +{ + git_SHA1_Update_unsafe(&ctx->sha1_unsafe, data, len); +} + +static void git_hash_sha1_final_unsafe(unsigned char *hash, git_hash_ctx *ctx) +{ + git_SHA1_Final_unsafe(hash, &ctx->sha1_unsafe); +} + +static void git_hash_sha1_final_oid_unsafe(struct object_id *oid, git_hash_ctx *ctx) +{ + git_SHA1_Final_unsafe(oid->hash, &ctx->sha1_unsafe); + memset(oid->hash + GIT_SHA1_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA1_RAWSZ); + oid->algo = GIT_HASH_SHA1; +} static void git_hash_sha256_init(git_hash_ctx *ctx) { @@ -189,6 +216,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_unknown_update, .final_fn = git_hash_unknown_final, .final_oid_fn = git_hash_unknown_final_oid, + .unsafe_init_fn = git_hash_unknown_init, + .unsafe_clone_fn = git_hash_unknown_clone, + .unsafe_update_fn = git_hash_unknown_update, + .unsafe_final_fn = git_hash_unknown_final, + .unsafe_final_oid_fn = git_hash_unknown_final_oid, .empty_tree = NULL, .empty_blob = NULL, .null_oid = NULL, @@ -204,6 +236,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_sha1_update, .final_fn = git_hash_sha1_final, .final_oid_fn = git_hash_sha1_final_oid, + .unsafe_init_fn = git_hash_sha1_init_unsafe, + .unsafe_clone_fn = git_hash_sha1_clone_unsafe, + .unsafe_update_fn = git_hash_sha1_update_unsafe, + .unsafe_final_fn = git_hash_sha1_final_unsafe, + .unsafe_final_oid_fn = git_hash_sha1_final_oid_unsafe, .empty_tree = &empty_tree_oid, .empty_blob = &empty_blob_oid, .null_oid = &null_oid_sha1, @@ -219,6 +256,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { .update_fn = git_hash_sha256_update, .final_fn = git_hash_sha256_final, .final_oid_fn = git_hash_sha256_final_oid, + .unsafe_init_fn = git_hash_sha256_init, + .unsafe_clone_fn = git_hash_sha256_clone, + .unsafe_update_fn = git_hash_sha256_update, + .unsafe_final_fn = git_hash_sha256_final, + .unsafe_final_oid_fn = git_hash_sha256_final_oid, .empty_tree = &empty_tree_oid_sha256, .empty_blob = &empty_blob_oid_sha256, .null_oid = &null_oid_sha256,
-- 2.46.2.636.g4b83dd05e9f