git/Documentation/config/uploadpack.txt
Glen Choo 779ea9303a Documentation: define protected configuration
For security reasons, there are config variables that are only trusted
when they are specified in certain configuration scopes, which are
sometimes referred to on-list as 'protected configuration' [1]. A future
commit will introduce another such variable, so let's define our terms
so that we can have consistent documentation and implementation.

In our documentation, define 'protected configuration' as the system,
global and command config scopes. As a shorthand, I will refer to
variables that are only respected in protected configuration as
'protected configuration only', but this term is not used in the
documentation.

This definition of protected configuration is based on whether or not
Git can reasonably protect the user by ignoring the configuration scope:

- System, global and command line config are considered protected
  because an attacker who has control over any of those can do plenty of
  harm without Git, so we gain very little by ignoring those scopes.

- On the other hand, local (and similarly, worktree) config are not
  considered protected because it is relatively easy for an attacker to
  control local config, e.g.:

  - On some shared user environments, a non-admin attacker can create a
    repository high up the directory hierarchy (e.g. C:\.git on
    Windows), and a user may accidentally use it when their PS1
    automatically invokes "git" commands.

    `safe.directory` prevents attacks of this form by making sure that
    the user intended to use the shared repository. It obviously
    shouldn't be read from the repository, because that would end up
    trusting the repository that Git was supposed to reject.

  - "git upload-pack" is expected to run in repositories that may not be
    controlled by the user. We cannot ignore all config in that
    repository (because "git upload-pack" would fail), but we can limit
    the risks by ignoring `uploadpack.packObjectsHook`.

Only `uploadpack.packObjectsHook` is 'protected configuration only'. The
following variables are intentionally excluded:

- `safe.directory` should be 'protected configuration only', but it does
  not technically fit the definition because it is not respected in the
  "command" scope. A future commit will fix this.

- `trace2.*` happens to read the same scopes as `safe.directory` because
  they share an implementation. However, this is not for security
  reasons; it is because we want to start tracing so early that
  repository-level config and "-c" are not available [2].

  This requirement is unique to `trace2.*`, so it does not makes sense
  for protected configuration to be subject to the same constraints.

[1] For example,
https://lore.kernel.org/git/6af83767-576b-75c4-c778-0284344a8fe7@github.com/
[2] https://lore.kernel.org/git/a0c89d0d-669e-bf56-25d2-cbb09b012e70@jeffhostetler.com/

Signed-off-by: Glen Choo <chooglen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-07-14 15:08:29 -07:00

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uploadpack.hideRefs::
This variable is the same as `transfer.hideRefs`, but applies
only to `upload-pack` (and so affects only fetches, not pushes).
An attempt to fetch a hidden ref by `git fetch` will fail. See
also `uploadpack.allowTipSHA1InWant`.
uploadpack.allowTipSHA1InWant::
When `uploadpack.hideRefs` is in effect, allow `upload-pack`
to accept a fetch request that asks for an object at the tip
of a hidden ref (by default, such a request is rejected).
See also `uploadpack.hideRefs`. Even if this is false, a client
may be able to steal objects via the techniques described in the
"SECURITY" section of the linkgit:gitnamespaces[7] man page; it's
best to keep private data in a separate repository.
uploadpack.allowReachableSHA1InWant::
Allow `upload-pack` to accept a fetch request that asks for an
object that is reachable from any ref tip. However, note that
calculating object reachability is computationally expensive.
Defaults to `false`. Even if this is false, a client may be able
to steal objects via the techniques described in the "SECURITY"
section of the linkgit:gitnamespaces[7] man page; it's best to
keep private data in a separate repository.
uploadpack.allowAnySHA1InWant::
Allow `upload-pack` to accept a fetch request that asks for any
object at all.
Defaults to `false`.
uploadpack.keepAlive::
When `upload-pack` has started `pack-objects`, there may be a
quiet period while `pack-objects` prepares the pack. Normally
it would output progress information, but if `--quiet` was used
for the fetch, `pack-objects` will output nothing at all until
the pack data begins. Some clients and networks may consider
the server to be hung and give up. Setting this option instructs
`upload-pack` to send an empty keepalive packet every
`uploadpack.keepAlive` seconds. Setting this option to 0
disables keepalive packets entirely. The default is 5 seconds.
uploadpack.packObjectsHook::
If this option is set, when `upload-pack` would run
`git pack-objects` to create a packfile for a client, it will
run this shell command instead. The `pack-objects` command and
arguments it _would_ have run (including the `git pack-objects`
at the beginning) are appended to the shell command. The stdin
and stdout of the hook are treated as if `pack-objects` itself
was run. I.e., `upload-pack` will feed input intended for
`pack-objects` to the hook, and expects a completed packfile on
stdout.
+
Note that this configuration variable is only respected when it is specified
in protected configuration (see <<SCOPES>>). This is a safety measure
against fetching from untrusted repositories.
uploadpack.allowFilter::
If this option is set, `upload-pack` will support partial
clone and partial fetch object filtering.
uploadpackfilter.allow::
Provides a default value for unspecified object filters (see: the
below configuration variable). If set to `true`, this will also
enable all filters which get added in the future.
Defaults to `true`.
uploadpackfilter.<filter>.allow::
Explicitly allow or ban the object filter corresponding to
`<filter>`, where `<filter>` may be one of: `blob:none`,
`blob:limit`, `object:type`, `tree`, `sparse:oid`, or `combine`.
If using combined filters, both `combine` and all of the nested
filter kinds must be allowed. Defaults to `uploadpackfilter.allow`.
uploadpackfilter.tree.maxDepth::
Only allow `--filter=tree:<n>` when `<n>` is no more than the value of
`uploadpackfilter.tree.maxDepth`. If set, this also implies
`uploadpackfilter.tree.allow=true`, unless this configuration
variable had already been set. Has no effect if unset.
uploadpack.allowRefInWant::
If this option is set, `upload-pack` will support the `ref-in-want`
feature of the protocol version 2 `fetch` command. This feature
is intended for the benefit of load-balanced servers which may
not have the same view of what OIDs their refs point to due to
replication delay.