Subject: [PATCH v2 00/12] Stop relying on SHA1 fallback for `the_hash_algo`

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 23 Apr 2024 07:07:20 +0200

Hi,

this is the second version of my patch series that causes us to stop
relying on the SHA1 default hash.

Changes compared to v1:

    - Various typo fixes in commit messages.

    - Added another patch that moves `validate_headref()` into "setup.c"
      to clarify that it is only used during repository discovery.

    - Indented a diff in a commit message so that git-am(1) is happy.

Thanks!

Patrick

Patrick Steinhardt (12):
  path: harden validation of HEAD with non-standard hashes
  path: move `validate_headref()` to its only user
  parse-options-cb: only abbreviate hashes when hash algo is known
  attr: don't recompute default attribute source
  attr: fix BUG() when parsing attrs outside of repo
  remote-curl: fix parsing of detached SHA256 heads
  builtin/rev-parse: allow shortening to more than 40 hex characters
  builtin/blame: don't access potentially unitialized `the_hash_algo`
  builtin/bundle: abort "verify" early when there is no repository
  builtin/diff: explicitly set hash algo when there is no repo
  builtin/shortlog: don't set up revisions without repo
  repository: stop setting SHA1 as the default object hash

 attr.c                     | 31 +++++++++++++++-------
 builtin/blame.c            |  5 ++--
 builtin/bundle.c           |  5 ++++
 builtin/diff.c             |  9 +++++++
 builtin/rev-parse.c        |  5 ++--
 builtin/shortlog.c         |  2 +-
 parse-options-cb.c         |  3 ++-
 path.c                     | 53 --------------------------------------
 path.h                     |  1 -
 remote-curl.c              | 19 +++++++++++++-
 repository.c               |  2 --
 setup.c                    | 53 ++++++++++++++++++++++++++++++++++++++
 t/t0003-attributes.sh      | 15 +++++++++++
 t/t0040-parse-options.sh   | 17 ++++++++++++
 t/t1500-rev-parse.sh       |  6 +++++
 t/t5550-http-fetch-dumb.sh | 15 +++++++++++
 16 files changed, 167 insertions(+), 74 deletions(-)

Range-diff against v1:
 1:  aa4d6f508b !  1:  a986b464d3 path: harden validation of HEAD with non-standard hashes
    @@ Commit message
         current version of Git doesn't understand yet. We'd still want to detect
         the repository as proper Git repository in that case, and we will fail
         eventually with a proper error message that the hash isn't understood
    -    when trying to set up the repostiory format.
    +    when trying to set up the repository format.
     
         It follows that we could just leave the current code intact, as in
         practice the code change doesn't have any user visible impact. But it
         also prepares us for `the_hash_algo` being unset when there is no
    -    repositroy.
    +    repository.
     
         Signed-off-by: Patrick Steinhardt <[email-masked]>
     
 -:  ---------- >  2:  a347c7e6ca path: move `validate_headref()` to its only user
 2:  5daaaed2b9 !  3:  c0a15b2fa6 parse-options-cb: only abbreviate hashes when hash algo is known
    @@ Commit message
         parse-options-cb: only abbreviate hashes when hash algo is known
     
         The `OPT__ABBREV()` option can be used to add an option that abbreviates
    -    object IDs. When given an length longer than `the_hash_algo->hexsz`,
    -    then it will instead set the length to that maximum length.
    +    object IDs. When given a length longer than `the_hash_algo->hexsz`, then
    +    it will instead set the length to that maximum length.
     
         It may not always be guaranteed that we have `the_hash_algo` initialized
    -    properly as the hash algortihm can only be set up after we have set up
    +    properly as the hash algorithm can only be set up after we have set up
         `the_repository`. In that case, the hash would always be truncated to
         the hex length of SHA1, which may not be what the user desires.
     
 3:  ae91a27ffc !  4:  1b5f904eed attr: don't recompute default attribute source
    @@ Commit message
         variable is the null object ID then we try to look up the attr source,
         otherwise we skip over it.
     
    -    This has approach is flawed though: the variable will never be set to
    +    This approach is flawed though: the variable will never be set to
         anything else but the null object ID in case there is no attr source.
         Consequently, we re-compute the information on every call. And in the
         worst case, when we silently ignore bad trees, this will cause us to try
 4:  53c8e1cd7c =  5:  26909daca4 attr: fix BUG() when parsing attrs outside of repo
 5:  32a429fb60 =  6:  0b99184f50 remote-curl: fix parsing of detached SHA256 heads
 6:  9cb7baa50c =  7:  ccfda3c2d2 builtin/rev-parse: allow shortening to more than 40 hex characters
 7:  e189a4ad15 =  8:  1813e7eb5c builtin/blame: don't access potentially unitialized `the_hash_algo`
 8:  bc4bda3508 =  9:  31182a1fc6 builtin/bundle: abort "verify" early when there is no repository
 9:  39e56dab62 ! 10:  78e19d0a1b builtin/diff: explicitly set hash algo when there is no repo
    @@ Commit message
         hashing the files that we are diffing so that we can print the "index"
         line:
     
    -    ```
    -    diff --git a/a b/b
    -    index 7898192..6178079 100644
    -    --- a/a
    -    +++ b/b
    -    @@ -1 +1 @@
    -    -a
    -    +b
    -    ```
    +        ```
    +        diff --git a/a b/b
    +        index 7898192..6178079 100644
    +        --- a/a
    +        +++ b/b
    +        @@ -1 +1 @@
    +        -a
    +        +b
    +        ```
     
         We implicitly use SHA1 to calculate the hash here, which is because
         `the_repository` gets initialized with SHA1 during the startup routine.
10:  508e28ed1e ! 11:  51bcddbc31 builtin/shortlog: don't set up revisions without repo
    @@ Commit message
         repository in that context, it is thus unsupported to pass any revisions
         as arguments.
     
    -    Reghardless of that we still end up calling `setup_revisions()`. While
    +    Regardless of that we still end up calling `setup_revisions()`. While
         that works alright, it is somewhat strange. Furthermore, this is about
         to cause problems when we unset the default object hash.
     
11:  f86a6ff3ba = 12:  e8126371e1 repository: stop setting SHA1 as the default object hash

base-commit: 21306a098c3f174ad4c2a5cddb9069ee27a548b0
-- 
2.45.0-rc0