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object-file: avoid ODB transaction when not writing objects 

In ce1661f9da (odb: add transaction interface, 2025-09-16), existing
ODB transaction logic is adapted to create a transaction interface
at the ODB layer. The intent here is for the ODB transaction
interface to eventually provide an object source agnostic means to
manage transactions.

An unintended consequence of this change though is that
`object-file.c:index_fd()` may enter the ODB transaction path even
when no object write is requested. In non-repository contexts, this
can result in a NULL dereference and segfault. One such case occurs
when running git-diff(1) outside of a repository with
"core.bigFileThreshold" forcing the streaming path in `index_fd()`:

        $ echo foo >foo
        $ echo bar >bar
        $ git -c core.bigFileThreshold=1 diff -- foo bar

In this scenario, the caller only needs to compute the object ID. Object
hashing does not require an ODB, so starting a transaction is both
unnecessary and invalid.

Fix the bug by avoiding the use of ODB transactions in `index_fd()` when
callers are only interested in computing the object hash.

Reported-by: Luca Stefani <luca.stefani.ge1@gmail.com>
Signed-off-by: Justin Tobler <jltobler@gmail.com>
[jc: adjusted to fd13909e (Merge branch 'jt/odb-transaction', 2025-10-02)]
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Justin Tobler 2026-04-07 15:17:30 -05:00 committed by Junio C Hamano
parent 9a2fb147f2
commit 7d8727ff0b
2 changed files with 48 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
object-file.c
View File

@ -1599,6 +1599,34 @@ static int index_blob_packfile_transaction(struct odb_transaction *transaction,
return 0;
}

static int hash_blob_stream(const struct git_hash_algo *hash_algo,
struct object_id *result_oid, int fd, size_t size)
{
unsigned char buf[16384];
struct git_hash_ctx ctx;
unsigned header_len;

header_len = format_object_header((char *)buf, sizeof(buf),
OBJ_BLOB, size);
hash_algo->init_fn(&ctx);
git_hash_update(&ctx, buf, header_len);

while (size) {
size_t rsize = size < sizeof(buf) ? size : sizeof(buf);
ssize_t read_result = read_in_full(fd, buf, rsize);

if ((read_result < 0) || ((size_t)read_result != rsize))
return -1;

git_hash_update(&ctx, buf, rsize);
size -= read_result;
}

git_hash_final_oid(result_oid, &ctx);

return 0;
}

int index_fd(struct index_state *istate, struct object_id *oid,
int fd, struct stat *st,
enum object_type type, const char *path, unsigned flags)
@ -1620,14 +1648,19 @@ int index_fd(struct index_state *istate, struct object_id *oid,
ret = index_core(istate, oid, fd, xsize_t(st->st_size),
type, path, flags);
} else {
struct odb_transaction *transaction;
if (flags & INDEX_WRITE_OBJECT) {
struct odb_transaction *transaction;

transaction = odb_transaction_begin(the_repository->objects);
ret = index_blob_packfile_transaction(the_repository->objects->transaction,
oid, fd,
xsize_t(st->st_size),
path, flags);
odb_transaction_commit(transaction);
transaction = odb_transaction_begin(the_repository->objects);
ret = index_blob_packfile_transaction(the_repository->objects->transaction,
oid, fd,
xsize_t(st->st_size),
path, flags);
odb_transaction_commit(transaction);
} else {
ret = hash_blob_stream(the_repository->hash_algo, oid,
fd, xsize_t(st->st_size));
}
}

close(fd);

8
t/t1517-outside-repo.sh
View File

@ -93,6 +93,14 @@ test_expect_success 'diff outside repository' '
test_cmp expect actual
'

test_expect_success 'hash object exceeding bigFileThreshold outside repository' '
(
cd non-repo &&
echo foo >foo &&
git -c core.bigFileThreshold=1 hash-object --stdin <foo
)
'

test_expect_success 'stripspace outside repository' '
nongit git stripspace -s </dev/null
'