CVE-2021-40330: git_connect_git(): forbid newlines in host and path · git/git@a02ea57

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git_connect_git(): forbid newlines in host and path

When we connect to a git:// server, we send an initial request that looks something like:

002dgit-upload-pack repo.git\0host=example.com

If the repo path contains a newline, then it’s included literally, and we get:

002egit-upload-pack repo .git\0host=example.com

This works fine if you really do have a newline in your repository name; the server side uses the pktline framing to parse the string, not newlines. However, there are many _other_ protocols in the wild that do parse on newlines, such as HTTP. So a carefully constructed git:// URL can actually turn into a valid HTTP request. For example:

git://localhost:1234/%0d%0a%0d%0aGET%20/%20HTTP/1.1 %0d%0aHost:localhost%0d%0a%0d%0a

becomes:

0050git-upload-pack / GET / HTTP/1.1 Host:localhost

host=localhost:1234

on the wire. Again, this isn’t a problem for a real Git server, but it does mean that feeding a malicious URL to Git (e.g., through a submodule) can cause it to make unexpected cross-protocol requests. Since repository names with newlines are presumably quite rare (and indeed, we already disallow them in git-over-http), let’s just disallow them over this protocol.

Hostnames could likewise inject a newline, but this is unlikely a problem in practice; we’d try resolving the hostname with a newline in it, which wouldn’t work. Still, it doesn’t hurt to err on the side of caution there, since we would not expect them to work in the first place.

The ssh and local code paths are unaffected by this patch. In both cases we’re trying to run upload-pack via a shell, and will quote the newline so that it makes it intact. An attacker can point an ssh url at an arbitrary port, of course, but unless there’s an actual ssh server there, we’d never get as far as sending our shell command anyway. We _could_ similarly restrict newlines in those protocols out of caution, but there seems little benefit to doing so.

The new test here is run alongside the git-daemon tests, which cover the same protocol, but it shouldn’t actually contact the daemon at all. In theory we could make the test more robust by setting up an actual repository with a newline in it (so that our clone would succeed if our new check didn’t kick in). But a repo directory with newline in it is likely not portable across all filesystems. Likewise, we could check git-daemon’s log that it was not contacted at all, but we do not currently record the log (and anyway, it would make the test racy with the daemon’s log write). We’ll just check the client-side stderr to make sure we hit the expected code path.

Reported-by: Harold Kim [email protected] Signed-off-by: Jeff King [email protected] Signed-off-by: Junio C Hamano [email protected]

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