Doc update on fetching and pushing.
* mm/push-social-engineering-attack-doc:
doc: mention transfer data leaks in more places
`refs/namespaces/bar/refs/heads/master` are still advertised as so-called
"have" lines. In order to match refs before stripping, add a `^` in front of
the ref name. If you combine `!` and `^`, `!` must be specified first.
++
+Even if you hide refs, a client may still be able to steal the target
+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.
transfer.unpackLimit::
When `fetch.unpackLimit` or `receive.unpackLimit` are
uploadarchive.allowUnreachable::
If true, allow clients to use `git archive --remote` to request
any tree, whether reachable from the ref tips or not. See the
- discussion in the `SECURITY` section of
+ discussion in the "SECURITY" section of
linkgit:git-upload-archive[1] for more details. Defaults to
`false`.
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`.
+ 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`.
+ 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.keepAlive::
When `upload-pack` has started `pack-objects`, there may be a
objects will eventually be removed by git's built-in housekeeping (see
linkgit:git-gc[1]).
+include::transfer-data-leaks.txt[]
+
BUGS
----
Using --recurse-submodules can only fetch new commits in already checked
would want to start over, you can recover with 'git reset'.
+include::transfer-data-leaks.txt[]
+
BUGS
----
Using --recurse-submodules can only fetch new commits in already checked
and so would be unreachable. As such, these commits would be removed by
a `git gc` command on the origin repository.
+include::transfer-data-leaks.txt[]
+
GIT
---
Part of the linkgit:git[1] suite
git clone ext::'git --namespace=foo %s /tmp/prefixed.git'
----------
-SECURITY
---------
-
-Anyone with access to any namespace within a repository can potentially
-access objects from any other namespace stored in the same repository.
-You can't directly say "give me object ABCD" if you don't have a ref to
-it, but you can do some other sneaky things like:
-
-. Claiming to push ABCD, at which point the server will optimize out the
- need for you to actually send it. Now you have a ref to ABCD and can
- fetch it (claiming not to have it, of course).
-
-. Requesting other refs, claiming that you have ABCD, at which point the
- server may generate deltas against ABCD.
-
-None of this causes a problem if you only host public repositories, or
-if everyone who may read one namespace may also read everything in every
-other namespace (for instance, if everyone in an organization has read
-permission to every repository).
+include::transfer-data-leaks.txt[]
--- /dev/null
+SECURITY
+--------
+The fetch and push protocols are not designed to prevent one side from
+stealing data from the other repository that was not intended to be
+shared. If you have private data that you need to protect from a malicious
+peer, your best option is to store it in another repository. This applies
+to both clients and servers. In particular, namespaces on a server are not
+effective for read access control; you should only grant read access to a
+namespace to clients that you would trust with read access to the entire
+repository.
+
+The known attack vectors are as follows:
+
+. The victim sends "have" lines advertising the IDs of objects it has that
+ are not explicitly intended to be shared but can be used to optimize the
+ transfer if the peer also has them. The attacker chooses an object ID X
+ to steal and sends a ref to X, but isn't required to send the content of
+ X because the victim already has it. Now the victim believes that the
+ attacker has X, and it sends the content of X back to the attacker
+ later. (This attack is most straightforward for a client to perform on a
+ server, by creating a ref to X in the namespace the client has access
+ to and then fetching it. The most likely way for a server to perform it
+ on a client is to "merge" X into a public branch and hope that the user
+ does additional work on this branch and pushes it back to the server
+ without noticing the merge.)
+
+. As in #1, the attacker chooses an object ID X to steal. The victim sends
+ an object Y that the attacker already has, and the attacker falsely
+ claims to have X and not Y, so the victim sends Y as a delta against X.
+ The delta reveals regions of X that are similar to Y to the attacker.
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