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@xxxxxxxxxxxx>
---
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
