Security of .git/config and .git/hooks
- Date: Mon, 2 Oct 2017 16:45:17 -0700
- From: Jonathan Nieder <jrnieder@xxxxxxxxx>
- Subject: Security of .git/config and .git/hooks
This topic has been mentioned on this mailing list before but I had
trouble finding a relevant reference. Links welcome.
Suppose that I add the following to .git/config in a repository on a
log = rm -fr /
fsck = rm -fr /
("rm -fr /" is of course a placeholder here.)
I then tell a sysadmin that git commands are producing strange output
and I am having trouble understanding what is going on. They may run
"git fsck" or "git log"; in either case, the output is passed to the
pager I configured, allowing me to run an arbitrary command using the
You might say that this is the sysadmin's fault, that they should have
read through .git/config before running any Git commands. But I don't
find it so easy to blame them.
A few related cases that might not seem so dated:
1. I put my repository in a zip file and ask a Git expert to help me
recover data from it, or
2. My repository is in a shared directory on NFS. Unless the
administrator setting that up is very careful, it is likely that
the least privileged user with write access to .git/config or
.git/hooks/ may be someone that I don't want to be able to run
arbitrary commands on behalf of the most privileged user working
in that repository.
A similar case to compare to is Linux's "perf" tool, which used to
respect a .perfconfig file from the current working directory.
Fortunately, nowadays "perf" only respects ~/.perfconfig and
Proposed fix: because of case (1), I would like a way to tell Git to
stop trusting any files in .git. That is:
1. Introduce a (configurable) list of "safe" configuration items that
can be set in .git/config and don't respect any others.
2. But what if I want to set a different pager per-repository?
I think we could do this using configuration "profiles".
My ~/.config/git/profiles/ directory would contain git-style
config files for repositories to include. Repositories could
path = ~/.config/git/profiles/fancy-log-pager
to make use of those settings. The facility (1) would
special-case this directory to allow it to set "unsafe" settings
since files there are assumed not to be under the control of an
3. Likewise for hooks: my ~/.config/git/hooks/ directory would
contain hooks for repositories to make use of. Repositories could
symlink to hook files from there to make use of them.
That would allow the configured hooks in ~/.config/git/hooks/ to
be easy to find and to upgrade in one place.
To help users migrate, when a hook is present and executable in
.git/hooks/, Git would print instructions for moving it to
~/.config/git/hooks/ and replacing it with a symlink after
For backward compatibility, this facility would be controlled by a
global configuration setting. If that setting is not enabled, then
the current, less safe behavior would remain.
One downside of (3) is its reliance on symlinks. Some alternatives:
3b. Use core.hooksPath configuration instead. Rely on (2).
3c. Introduce new hook.* configuration to be used instead of hook
scripts. Rely on (2).