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From bf27a288adce36e2a57e26146d18c224ebc745be Mon Sep 17 00:00:00 2001
From: Oliver Reiche <oliver.reiche@huawei.com>
Date: Wed, 3 Aug 2022 16:27:58 +0200
Subject: [PATCH] Do not register fake repository as owner of ODB
Accessing ODB is guaranteed to be thread-safe. Registering a
fake repository (created via git_repository_wrap_odb()) may
not register itself as owner of the ODB in order to maintain
that guarantee. Otherwise, accessing objects from ODB will
try to obtain the cache from the owning repository (via
odb_cache()) and produce a race if this ODB is concurrently
used to create fake repositories in other threads.
Consequently, operations on fake repositories will interact
with the ODB's cache instead of the repository's cache.
---
include/git2/sys/repository.h | 3 ++-
src/repository.c | 16 +++++++++-------
tests/odb/backend/nobackend.c | 2 +-
tests/repo/setters.c | 23 ++++++++++++++++++++++-
4 files changed, 34 insertions(+), 10 deletions(-)
diff --git a/include/git2/sys/repository.h b/include/git2/sys/repository.h
index 892be6692..33bc5051f 100644
--- a/include/git2/sys/repository.h
+++ b/include/git2/sys/repository.h
@@ -97,9 +97,10 @@ GIT_EXTERN(int) git_repository_set_config(git_repository *repo, git_config *conf
*
* @param repo A repository object
* @param odb An ODB object
+ * @param set_owner Register repository as owner of ODB
* @return 0 on success, or an error code
*/
-GIT_EXTERN(int) git_repository_set_odb(git_repository *repo, git_odb *odb);
+GIT_EXTERN(int) git_repository_set_odb(git_repository *repo, git_odb *odb, bool set_owner);
/**
* Set the Reference Database Backend for this repository
diff --git a/src/repository.c b/src/repository.c
index 513dbd61f..9e5aa6a16 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -86,10 +86,12 @@ git_buf git_repository__reserved_names_posix[] = {
};
size_t git_repository__reserved_names_posix_len = 1;
-static void set_odb(git_repository *repo, git_odb *odb)
+static void set_odb(git_repository *repo, git_odb *odb, bool set_owner)
{
if (odb) {
- GIT_REFCOUNT_OWN(odb, repo);
+ if (set_owner) {
+ GIT_REFCOUNT_OWN(odb, repo);
+ }
GIT_REFCOUNT_INC(odb);
}
@@ -150,7 +152,7 @@ int git_repository__cleanup(git_repository *repo)
set_config(repo, NULL);
set_index(repo, NULL);
- set_odb(repo, NULL);
+ set_odb(repo, NULL, /*set_owner=*/true);
set_refdb(repo, NULL);
return 0;
@@ -722,7 +724,7 @@ static int _git_repository_open_ext_from_env(
goto error;
if (odb)
- git_repository_set_odb(repo, odb);
+ git_repository_set_odb(repo, odb, /*set_owner=*/true);
error = git__getenv(&alts_buf, "GIT_ALTERNATE_OBJECT_DIRECTORIES");
if (error == GIT_ENOTFOUND) {
@@ -932,7 +934,7 @@ int git_repository_wrap_odb(git_repository **repo_out, git_odb *odb)
repo = repository_alloc();
GIT_ERROR_CHECK_ALLOC(repo);
- git_repository_set_odb(repo, odb);
+ git_repository_set_odb(repo, odb, /*set_owner=*/false);
*repo_out = repo;
return 0;
@@ -1139,10 +1141,10 @@ int git_repository_odb(git_odb **out, git_repository *repo)
return 0;
}
-int git_repository_set_odb(git_repository *repo, git_odb *odb)
+int git_repository_set_odb(git_repository *repo, git_odb *odb, bool set_owner)
{
assert(repo && odb);
- set_odb(repo, odb);
+ set_odb(repo, odb, set_owner);
return 0;
}
diff --git a/tests/odb/backend/nobackend.c b/tests/odb/backend/nobackend.c
index 7484d423b..d46a7fed9 100644
--- a/tests/odb/backend/nobackend.c
+++ b/tests/odb/backend/nobackend.c
@@ -16,7 +16,7 @@ void test_odb_backend_nobackend__initialize(void)
cl_git_pass(git_refdb_new(&refdb, _repo));
git_repository_set_config(_repo, config);
- git_repository_set_odb(_repo, odb);
+ git_repository_set_odb(_repo, odb, /*set_owner=*/true);
git_repository_set_refdb(_repo, refdb);
/* The set increases the refcount and we don't want them anymore */
diff --git a/tests/repo/setters.c b/tests/repo/setters.c
index 1fac627f6..bf1b31783 100644
--- a/tests/repo/setters.c
+++ b/tests/repo/setters.c
@@ -94,7 +94,28 @@ void test_repo_setters__setting_a_new_odb_on_a_repo_which_already_loaded_one_pro
cl_git_pass(git_odb_open(&new_odb, "./testrepo.git/objects"));
cl_assert(((git_refcount *)new_odb)->refcount.val == 1);
- git_repository_set_odb(repo, new_odb);
+ git_repository_set_odb(repo, new_odb, /*set_owner=*/true);
+ cl_assert(((git_refcount *)new_odb)->refcount.val == 2);
+
+ git_repository_free(repo);
+ cl_assert(((git_refcount *)new_odb)->refcount.val == 1);
+
+ git_odb_free(new_odb);
+
+ /*
+ * Ensure the cleanup method won't try to free the repo as it's already been taken care of
+ */
+ repo = NULL;
+}
+
+void test_repo_setters__setting_a_new_odb_on_a_non_owner_repo_which_already_loaded_one_properly_honors_the_refcount(void)
+{
+ git_odb *new_odb;
+
+ cl_git_pass(git_odb_open(&new_odb, "./testrepo.git/objects"));
+ cl_assert(((git_refcount *)new_odb)->refcount.val == 1);
+
+ git_repository_set_odb(repo, new_odb, /*set_owner=*/false);
cl_assert(((git_refcount *)new_odb)->refcount.val == 2);
git_repository_free(repo);
--
2.25.1
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