[PATCH v2 0/8] hash: introduce unsafe_hash_algo(), drop unsafe_ variants
- From
Taylor Blau <me@ttaylorr.com>
- Date
- Jan 8, 2025, 19:14 UTC
- Message-ID
- <cover.1736363652.git.me@ttaylorr.com>
- In-Reply-To
- <cover.1732130001.git.me@ttaylorr.com>
(This series is rebased on 'master', which is 14650065b7 (RelNotes/2.48.0: fix typos etc., 2025-01-07) at the time of writing).
The bulk of this series is unchanged since last time, but a new seventh patch that further hardens the hashfile_checkpoint callers on top of Patrick's recent series[1].
The original cover letter is as follows:
------------
This series implements an idea discussed in [2] which suggests that we introduce a way to access a wrapped version of a 'struct git_hash_algo' which represents the unsafe variant of that algorithm, rather than having individual unsafe_ functions (like unsafe_init_fn() versus init_fn(), etc.).
This approach is relatively straightforward to implement, and removes a significant deficiency in the original implementation of unsafe/non-cryptographic hash functions by making it impossible to switch between safe- and unsafe variants of hash functions. It also cleans up the sha1-unsafe test helper's implementation by removing a large number of "if (unsafe)"-style conditionals.
The series is laid out as follows:
* The first two patches prepare the hashfile API for the upcoming
change: csum-file: store the hash algorithm as a struct field
csum-file.c: extract algop from hashfile_checksum_valid() * The next patch implements the new 'unsafe_hash_algo()' function at
the heart of this series' approach:hash.h: introduce `unsafe_hash_algo()`
* The next two patches convert existing callers to use the new
'unsafe_hash_algo()' function, instead of switching between safe and
unsafe_ variants of individual functions: csum-file.c: use unsafe_hash_algo()
t/helper/test-hash.c: use unsafe_hash_algo() * The final patch drops the unsafe_ function variants following all
callers being converted to use the new pattern:hash.h: drop unsafe_ function variants
Thanks in advance for your review!
[1]: https://lore.kernel.org/git/20241230-pks-meson-sha1-unsafe-v1-0-efb276e171f5@pks.im/ [2]: https://lore.kernel.org/git/20241107013915.GA961214@coredump.intra.peff.net/
Taylor Blau (8): t/helper/test-tool: implement sha1-unsafe helper csum-file: store the hash algorithm as a struct field csum-file.c: extract algop from hashfile_checksum_valid() hash.h: introduce `unsafe_hash_algo()` csum-file.c: use unsafe_hash_algo() t/helper/test-hash.c: use unsafe_hash_algo() csum-file: introduce hashfile_checkpoint_init() hash.h: drop unsafe_ function variants
builtin/fast-import.c | 2 +- bulk-checkin.c | 9 ++++++--- csum-file.c | 40 +++++++++++++++++++++++++--------------- csum-file.h | 2 ++ hash.h | 20 +++++--------------- object-file.c | 41 ++++++++++++++++++++++++++--------------- t/helper/test-hash.c | 4 +++- t/helper/test-sha1.c | 7 ++++++- t/helper/test-sha1.sh | 38 ++++++++++++++++++++++---------------- t/helper/test-sha256.c | 2 +- t/helper/test-tool.c | 1 + t/helper/test-tool.h | 3 ++- 12 files changed, 100 insertions(+), 69 deletions(-)
Range-diff against v1:
2: d8c1fc78b57 ! 1: 4c1523a04f1 t/helper/test-tool: implement sha1-unsafe helper
@@ Metadata
## Commit message ##
t/helper/test-tool: implement sha1-unsafe helper
- Add a new helper similar to 't/helper/test-tool sha1' called instead
- "sha1-unsafe" which uses the unsafe variant of Git's SHA-1 wrappers.
+ With the new "unsafe" SHA-1 build knob, it is convenient to have a
+ test-tool that can exercise Git's unsafe SHA-1 wrappers for testing,
+ similar to 't/helper/test-tool sha1'.
- While we're at it, modify the test-sha1.sh script to exercise both
- the sha1 and sha1-unsafe test tools to ensure that both produce the
- expected hash values.
+ Implement that helper by altering the implementation of that test-tool
+ (in cmd_hash_impl(), which is generic and parameterized over different
+ hash functions) to conditionally run the unsafe variants of the chosen
+ hash function, and expose the new behavior via a new 'sha1-unsafe' test
+ helper.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
+ ## t/helper/test-hash.c ##
+@@
+ #include "test-tool.h"
+ #include "hex.h"
+
+-int cmd_hash_impl(int ac, const char **av, int algo)
++int cmd_hash_impl(int ac, const char **av, int algo, int unsafe)
+ {
+ git_hash_ctx ctx;
+ unsigned char hash[GIT_MAX_HEXSZ];
+@@ t/helper/test-hash.c: int cmd_hash_impl(int ac, const char **av, int algo)
+ die("OOPS");
+ }
+
+- algop->init_fn(&ctx);
++ if (unsafe)
++ algop->unsafe_init_fn(&ctx);
++ else
++ algop->init_fn(&ctx);
+
+ while (1) {
+ ssize_t sz, this_sz;
+@@ t/helper/test-hash.c: int cmd_hash_impl(int ac, const char **av, int algo)
+ }
+ if (this_sz == 0)
+ break;
+- algop->update_fn(&ctx, buffer, this_sz);
++ if (unsafe)
++ algop->unsafe_update_fn(&ctx, buffer, this_sz);
++ else
++ algop->update_fn(&ctx, buffer, this_sz);
+ }
+- algop->final_fn(hash, &ctx);
++ if (unsafe)
++ algop->unsafe_final_fn(hash, &ctx);
++ else
++ algop->final_fn(hash, &ctx);
+
+ if (binary)
+ fwrite(hash, 1, algop->rawsz, stdout);
+
## t/helper/test-sha1.c ##
+@@
+
+ int cmd__sha1(int ac, const char **av)
+ {
+- return cmd_hash_impl(ac, av, GIT_HASH_SHA1);
++ return cmd_hash_impl(ac, av, GIT_HASH_SHA1, 0);
+ }
+
+ int cmd__sha1_is_sha1dc(int argc UNUSED, const char **argv UNUSED)
@@ t/helper/test-sha1.c: int cmd__sha1_is_sha1dc(int argc UNUSED, const char **argv UNUSED)
#endif
return 1;
@@ t/helper/test-sha1.sh
da39a3ee5e6b4b0d3255bfef95601890afd80709 0
3f786850e387550fdab836ed7e6dc881de23001b 0 a
+ ## t/helper/test-sha256.c ##
+@@
+
+ int cmd__sha256(int ac, const char **av)
+ {
+- return cmd_hash_impl(ac, av, GIT_HASH_SHA256);
++ return cmd_hash_impl(ac, av, GIT_HASH_SHA256, 0);
+ }
+
## t/helper/test-tool.c ##
@@ t/helper/test-tool.c: static struct test_cmd cmds[] = {
{ "serve-v2", cmd__serve_v2 },
@@ t/helper/test-tool.h: int cmd__scrap_cache_tree(int argc, const char **argv);
int cmd__sha256(int argc, const char **argv);
int cmd__sigchain(int argc, const char **argv);
int cmd__simple_ipc(int argc, const char **argv);
+@@ t/helper/test-tool.h: int cmd__windows_named_pipe(int argc, const char **argv);
+ #endif
+ int cmd__write_cache(int argc, const char **argv);
+
+-int cmd_hash_impl(int ac, const char **av, int algo);
++int cmd_hash_impl(int ac, const char **av, int algo, int unsafe);
+
+ #endif
3: 380133a1142 = 2: 99cc44895b5 csum-file: store the hash algorithm as a struct field
4: e5076f003bf = 3: 1ffab2f8289 csum-file.c: extract algop from hashfile_checksum_valid()
5: 17f92dba34b = 4: 99dcbe2e716 hash.h: introduce `unsafe_hash_algo()`
6: 0d8e12599e2 = 5: 2dcc2aa6803 csum-file.c: use unsafe_hash_algo()
7: a49a41703e2 = 6: a2b9ef03080 t/helper/test-hash.c: use unsafe_hash_algo()
1: 0e2fcee6894 ! 7: 94c07fd8a55 t/helper/test-sha1: prepare for an unsafe mode
@@ Metadata
Author: Taylor Blau <me@ttaylorr.com>
## Commit message ##
- t/helper/test-sha1: prepare for an unsafe mode
+ csum-file: introduce hashfile_checkpoint_init()
- With the new "unsafe" SHA-1 build knob, it would be convenient to have
- a test-tool that can exercise Git's unsafe SHA-1 wrappers for testing,
- similar to 't/helper/test-tool sha1'.
+ In 106140a99f (builtin/fast-import: fix segfault with unsafe SHA1
+ backend, 2024-12-30) and 9218c0bfe1 (bulk-checkin: fix segfault with
+ unsafe SHA1 backend, 2024-12-30), we observed the effects of failing to
+ initialize a hashfile_checkpoint with the same hash function
+ implementation as is used by the hashfile it is used to checkpoint.
- Prepare for such a helper by altering the implementation of that
- test-tool (in cmd_hash_impl(), which is generic and parameterized over
- different hash functions) to conditionally run the unsafe variants of
- the chosen hash function.
+ While both 106140a99f and 9218c0bfe1 work around the immediate crash,
+ changing the hash function implementation within the hashfile API to,
+ for example, the non-unsafe variant would re-introduce the crash. This
+ is a result of the tight coupling between initializing hashfiles and
+ hashfile_checkpoints.
- The following commit will add a new test-tool which makes use of this
- new parameter.
+ Introduce and use a new function which ensures that both parts of a
+ hashfile and hashfile_checkpoint pair use the same hash function
+ implementation to avoid such crashes.
+ A few things worth noting:
+
+ - In the change to builtin/fast-import.c::stream_blob(), we can see
+ that by removing the explicit reference to
+ 'the_hash_algo->unsafe_init_fn()', we are hardened against the
+ hashfile API changing away from the_hash_algo (or its unsafe
+ variant) in the future.
+
+ - The bulk-checkin code no longer needs to explicitly zero-initialize
+ the hashfile_checkpoint, since it is now done as a result of calling
+ 'hashfile_checkpoint_init()'.
+
+ - Also in the bulk-checkin code, we add an additional call to
+ prepare_to_stream() outside of the main loop in order to initialize
+ 'state->f' so we know which hash function implementation to use when
+ calling 'hashfile_checkpoint_init()'.
+
+ This is OK, since subsequent 'prepare_to_stream()' calls are noops.
+ However, we only need to call 'prepare_to_stream()' when we have the
+ HASH_WRITE_OBJECT bit set in our flags. Without that bit, calling
+ 'prepare_to_stream()' does not assign 'state->f', so we have nothing
+ to initialize.
+
+ - Other uses of the 'checkpoint' in 'deflate_blob_to_pack()' are
+ appropriately guarded.
+
+ Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
- ## t/helper/test-hash.c ##
-@@
- #include "test-tool.h"
- #include "hex.h"
+ ## builtin/fast-import.c ##
+@@ builtin/fast-import.c: static void stream_blob(uintmax_t len, struct object_id *oidout, uintmax_t mark)
+ || (pack_size + PACK_SIZE_THRESHOLD + len) < pack_size)
+ cycle_packfile();
--int cmd_hash_impl(int ac, const char **av, int algo)
-+int cmd_hash_impl(int ac, const char **av, int algo, int unsafe)
- {
+- the_hash_algo->unsafe_init_fn(&checkpoint.ctx);
++ hashfile_checkpoint_init(pack_file, &checkpoint);
+ hashfile_checkpoint(pack_file, &checkpoint);
+ offset = checkpoint.offset;
+
+
+ ## bulk-checkin.c ##
+@@ bulk-checkin.c: static int deflate_blob_to_pack(struct bulk_checkin_packfile *state,
git_hash_ctx ctx;
- unsigned char hash[GIT_MAX_HEXSZ];
-@@ t/helper/test-hash.c: int cmd_hash_impl(int ac, const char **av, int algo)
- die("OOPS");
- }
+ unsigned char obuf[16384];
+ unsigned header_len;
+- struct hashfile_checkpoint checkpoint = {0};
++ struct hashfile_checkpoint checkpoint;
+ struct pack_idx_entry *idx = NULL;
-- algop->init_fn(&ctx);
-+ if (unsafe)
-+ algop->unsafe_init_fn(&ctx);
-+ else
-+ algop->init_fn(&ctx);
+ seekback = lseek(fd, 0, SEEK_CUR);
+@@ bulk-checkin.c: static int deflate_blob_to_pack(struct bulk_checkin_packfile *state,
+ OBJ_BLOB, size);
+ the_hash_algo->init_fn(&ctx);
+ the_hash_algo->update_fn(&ctx, obuf, header_len);
+- the_hash_algo->unsafe_init_fn(&checkpoint.ctx);
+
+ /* Note: idx is non-NULL when we are writing */
+- if ((flags & HASH_WRITE_OBJECT) != 0)
++ if ((flags & HASH_WRITE_OBJECT) != 0) {
+ CALLOC_ARRAY(idx, 1);
+
++ prepare_to_stream(state, flags);
++ hashfile_checkpoint_init(state->f, &checkpoint);
++ }
++
+ already_hashed_to = 0;
while (1) {
- ssize_t sz, this_sz;
-@@ t/helper/test-hash.c: int cmd_hash_impl(int ac, const char **av, int algo)
- }
- if (this_sz == 0)
- break;
-- algop->update_fn(&ctx, buffer, this_sz);
-+ if (unsafe)
-+ algop->unsafe_update_fn(&ctx, buffer, this_sz);
-+ else
-+ algop->update_fn(&ctx, buffer, this_sz);
- }
-- algop->final_fn(hash, &ctx);
-+ if (unsafe)
-+ algop->unsafe_final_fn(hash, &ctx);
-+ else
-+ algop->final_fn(hash, &ctx);
-
- if (binary)
- fwrite(hash, 1, algop->rawsz, stdout);
- ## t/helper/test-sha1.c ##
-@@
-
- int cmd__sha1(int ac, const char **av)
- {
-- return cmd_hash_impl(ac, av, GIT_HASH_SHA1);
-+ return cmd_hash_impl(ac, av, GIT_HASH_SHA1, 0);
+ ## csum-file.c ##
+@@ csum-file.c: struct hashfile *hashfd_throughput(int fd, const char *name, struct progress *tp
+ return hashfd_internal(fd, name, tp, 8 * 1024);
}
- int cmd__sha1_is_sha1dc(int argc UNUSED, const char **argv UNUSED)
-
- ## t/helper/test-sha256.c ##
-@@
-
- int cmd__sha256(int ac, const char **av)
++void hashfile_checkpoint_init(struct hashfile *f,
++ struct hashfile_checkpoint *checkpoint)
++{
++ memset(checkpoint, 0, sizeof(*checkpoint));
++ f->algop->init_fn(&checkpoint->ctx);
++}
++
+ void hashfile_checkpoint(struct hashfile *f, struct hashfile_checkpoint *checkpoint)
{
-- return cmd_hash_impl(ac, av, GIT_HASH_SHA256);
-+ return cmd_hash_impl(ac, av, GIT_HASH_SHA256, 0);
- }
+ hashflush(f);
- ## t/helper/test-tool.h ##
-@@ t/helper/test-tool.h: int cmd__windows_named_pipe(int argc, const char **argv);
- #endif
- int cmd__write_cache(int argc, const char **argv);
+ ## csum-file.h ##
+@@ csum-file.h: struct hashfile_checkpoint {
+ git_hash_ctx ctx;
+ };
--int cmd_hash_impl(int ac, const char **av, int algo);
-+int cmd_hash_impl(int ac, const char **av, int algo, int unsafe);
++void hashfile_checkpoint_init(struct hashfile *, struct hashfile_checkpoint *);
+ void hashfile_checkpoint(struct hashfile *, struct hashfile_checkpoint *);
+ int hashfile_truncate(struct hashfile *, struct hashfile_checkpoint *);
- #endif
8: 4081ad08549 = 8: f5579883816 hash.h: drop unsafe_ function variantsbase-commit: 14650065b76b28d3cfa9453356ac5669b19e706e
-- 2.48.0.rc2.33.gaab3d23ed4c