From a8dd3821fe4fcf1524537ef97e4f5e2cf68ce949 Mon Sep 17 00:00:00 2001 From: Taylor Blau Date: Thu, 23 Jan 2025 12:34:39 -0500 Subject: csum-file: introduce hashfile_checkpoint_init() 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. 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. 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 Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- csum-file.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'csum-file.c') diff --git a/csum-file.c b/csum-file.c index ebffc80ef7..232121f415 100644 --- a/csum-file.c +++ b/csum-file.c @@ -206,6 +206,13 @@ struct hashfile *hashfd_throughput(int fd, const char *name, struct progress *tp return hashfd_internal(fd, name, tp, 8 * 1024); } +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) { hashflush(f); -- cgit 1.2.3-korg