Mercurial: Changelog

hgweb: always perform permissions checks on protocol commands (BC) (SEC) Previously, the HTTP request handling code would only perform permissions checking on a wire protocol command if that wire protocol command defined its permissions / operation type. This meant that commands (possibly provided by extensions) not defining their operation type would bypass permissions check. This could lead to exfiltration of data from servers and mutating repositories that were supposed to be read-only. This security issue has been present since the permissions table was introduced by d3147b4e3e8a in 2008. This commit changes the behavior of the HTTP server to always perform permissions checking for protocol requests. If an explicit permission for a wire protocol command is not defined, the server assumes the command can be used for writing and governs access accordingly. .. bc:: Wire protocol commands not defining their operation type in ``wireproto.PERMISSIONS`` are now assumed to be used for "push" operations and access control to run those commands is now enforced accordingly.

wireproto: check permissions when executing "batch" command (BC) (SEC) For as long as the "batch" command has existed (introduced by bd88561afb4b and first released as part of Mercurial 1.9), that command (like most wire commands introduced after 2008) lacked an entry in the hgweb permissions table. And since we don't verify permissions if an entry is missing from the permissions table, this meant that executing a command via "batch" would bypass all permissions checks. The security implications are significant: a Mercurial HTTP server would allow writes via "batch" wire protocol commands as long as the HTTP request were processed by Mercurial and the process running the Mercurial HTTP server had write access to the repository. The Mercurial defaults of servers being read-only and the various web.* config options to define access control were bypassed. In addition, "batch" could be used to exfiltrate data from servers that were configured to not allow read access. Both forms of permissions bypass could be mitigated to some extent by using HTTP authentication. This would prevent HTTP requests from hitting Mercurial's server logic. However, any authenticated request would still be able to bypass permissions checks via "batch" commands. The easiest exploit was to send "pushkey" commands via "batch" and modify the state of bookmarks, phases, and obsolescence markers. However, I suspect a well-crafted HTTP request could trick the server into running the "unbundle" wire protocol command, effectively performing a full `hg push` to create new changesets on the remote. This commit plugs this gaping security hole by having the "batch" command perform permissions checking on each sub-command that is being batched. We do this by threading a permissions checking callable all the way to the protocol handler. The threading is a bit hacky from a code perspective. But it preserves API compatibility, which is the proper thing to do on the stable branch. One of the subtle things we do is assume that a command with an undefined permission is a "push" command. This is the safest thing to do from a security perspective: we don't want to take chances that a command could perform a write even though the server is configured to not allow writes. As the test changes demonstrate, it is no longer possible to bypass permissions via the "batch" wire protocol command. .. bc:: The "batch" wire protocol command now enforces permissions of each invoked sub-command. Wire protocol commands must define their operation type or the "batch" command will assume they can write data and will prevent their execution on HTTP servers unless the HTTP request method is POST, the server is configured to allow pushes, and the (possibly authenticated) HTTP user is authorized to perform a push.

wireproto: declare operation type for most commands (BC) (SEC) The permissions model of hgweb relies on a dictionary to declare the operation associated with each command - either "pull" or "push." This dictionary was established by d3147b4e3e8a in 2008. Unfortunately, we neglected to update this dictionary as new wire protocol commands were introduced. This commit defines the operations of most wire protocol commands in the permissions dictionary. The "batch" command is omitted because it is special and requires a more complex solution. Since permissions checking is skipped unless a command has an entry in this dictionary (this security issue will be addressed in a subsequent commit), the practical effect of this change is that various wire protocol commands now HTTP 401 if web.deny_read or web.allow-pull, etc are set to deny access. This is reflected by test changes. Note how various `hg pull` and `hg push` operations now fail before discovery. (They fail during the initial "capabilities" request.) This change fixes a security issue where built-in wire protocol commands would return repository data even if the web config were configured to deny access to that data. I'm on the fence as to whether we should HTTP 401 the capabilities request. On one hand, it can expose repository metadata and can tell callers things like what version of Mercurial the server is running. On the other hand, a client may need to know the capabilities in order to authenticate in a follow-up request. It appears that Mercurial clients handle the HTTP 401 on *any* protocol request, so we should be OK sending a 401 for "capabilities." But if this causes problems, it should be possible to allow "capabilities" to always work. .. bc:: Various read-only wire protocol commands now return HTTP 401 Unauthorized if the hgweb configuration denies read/pull access to the repository. Previously, various wire protocol commands would still work and return data if read access was disabled.

wireproto: move command permissions dict out of hgweb_mod The operation type associated with wire protocol commands is supposed to be defined in a dictionary so it can be used for permissions checking. Since this metadata is closely associated with wire protocol commands themselves, it makes sense to define it in the same module where wire protocol commands are defined. This commit moves hgweb_mod.perms to wireproto.PERMISSIONS and updates most references in the code to use the new home. The old symbol remains an alias for the new symbol. Tests pass with the code pointing at the old symbol. So this should be API compatible for extensions. As part of the code move, we split up the assignment to the dict so it is next to the @wireprotocommand. This reinforces that a @wireprotocommand should have an entry in this dict. In the future, we'll want to declare permissions as part of the @wireprotocommand decorator. But this isn't appropriate for the stable branch.