# git submodule: update=!command 10 messages from 2015-03-17 to 2015-03-18. Participants: Ryan Lortie, Jeff King, Junio C Hamano, Chris Packham. Thread: https://gitlist.dev/t/38834 ## Ryan Lortie, 2015-03-17 19:28 Subject: git submodule: update=!command Message-ID: <1426620537.1785877.241673949.72FB3B40@webmail.messagingengine.com> URL: https://gitlist.dev/e/1426620537.1785877.241673949.72FB3B40%40webmail.messagingengine.com ``` karaj, 'man git-submodule' contains mention (in one place) that: Setting the key submodule.$name.update to !command will cause command to be run. This is not documented in 'man gitmodules' (which documents the other possible values for the 'update' key) nor in 'man git-config' which also mentions the 'update' key (but refers readers to the two other pages). This feature is scary. The idea that arbitrary code could be executed on my machine when I run innocent-looking git commands, based on the content of the .gitmodules file is enough to give pause to anybody. Fortunately, it seems that (for now?) this is not really the case. 'git submodule init' will copy the values of the 'update' key from .gitmodules to your local git config, but only if they are one of "none", "checkout", "merge" or "rebase". So, I guess I'm asking two things. The first is a question about git's basic policy with respect to things like this. I hope that it's safe to assume that running 'git' commands on repositories downloaded from potentially-hostile places will never result in the authors of those repositories being able to run code on my machine. If that is true then, the second request would be to spell this out more explicitly in the relevant documentation. I'm happy to write a patch to do that, if it is deemed appropriate. Thanks in advance. Cheers ``` ## Jeff King, 2015-03-17 19:50 Subject: Re: git submodule: update=!command Message-ID: <20150317195030.GA18725@peff.net> URL: https://gitlist.dev/e/20150317195030.GA18725%40peff.net In-Reply-To: <1426620537.1785877.241673949.72FB3B40@webmail.messagingengine.com> ``` On Tue, Mar 17, 2015 at 03:28:57PM -0400, Ryan Lortie wrote: > The first is a question about git's basic policy with respect to things > like this. I hope that it's safe to assume that running 'git' commands > on repositories downloaded from potentially-hostile places will never > result in the authors of those repositories being able to run code on my > machine. Definitely, our policy is that downloading a git repository should not result in arbitrary code being run. If there is a case of that, it would be a serious security bug. I am not an expert on submodules, but I think the security module there is: 1. You can do whatever you like in submodule.*.update entries in .git/config, including arbitrary code. Nobody but the user can write to it. 2. The submodule code may migrate entries from .gitmodules into .git/config, but does so with an allow-known-good whitelist (see git-submodule.sh lines 622-637). So AFAICT there's no bug here, and the system is working as designed. It might be worth mentioning that restriction in the submodule documentation, if only to prevent non-malicious people from wondering why adding "!foo" does not work in .gitmodules. > If that is true then, the second request would be to spell this out more > explicitly in the relevant documentation. I'm happy to write a patch to > do that, if it is deemed appropriate. Yeah, spelling out the security model more explicitly would be good. There is also some subtlety around hooks. Doing: git clone user@host:/path/to/repo.git local should never run code controlled by "repo.git" as "user@host". But doing: ssh user@host 'cd /path/to/repo.git && git log' will respect the .git/config in repo.git, which may include arbitrary commands. -Peff ``` ## Ryan Lortie, 2015-03-17 20:48 Subject: Re: git submodule: update=!command Message-ID: <1426625302.1806008.241713717.52A37086@webmail.messagingengine.com> URL: https://gitlist.dev/e/1426625302.1806008.241713717.52A37086%40webmail.messagingengine.com In-Reply-To: <20150317195030.GA18725@peff.net> ``` On Tue, Mar 17, 2015, at 15:50, Jeff King wrote: > Yeah, spelling out the security model more explicitly would be good. Please see the attached patch. Cheers From a6d70056f21f039db8676f72a1deca00c39121bd Mon Sep 17 00:00:00 2001 From: Ryan Lortie Date: Tue, 17 Mar 2015 16:29:51 -0400 Subject: [PATCH] docs: clarify !command submodule update policy Clarify that the !command submodule update policy is not available from .gitmodules files. This should help calm any fears people have about the security implications of this otherwise scary-looking feature. Signed-off-by: Ryan Lortie --- Documentation/git-submodule.txt | 10 +++++++--- Documentation/gitmodules.txt | 11 ++++++++--- 2 files changed, 15 insertions(+), 6 deletions(-) diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt index 8e6af65..a033e26 100644 --- a/Documentation/git-submodule.txt +++ b/Documentation/git-submodule.txt @@ -159,9 +159,13 @@ update:: This will make the submodules HEAD be detached unless `--rebase` or `--merge` is specified or the key `submodule.$name.update` is set to `rebase`, `merge` or `none`. `none` can be overridden by specifying - `--checkout`. Setting the key `submodule.$name.update` to `!command` - will cause `command` to be run. `command` can be any arbitrary shell - command that takes a single argument, namely the sha1 to update to. + `--checkout`. ++ +Setting the key `submodule.$name.update` in `.git/config` to +`!command` will cause `command` to be run. `command` can be any +arbitrary shell command that takes a single argument, namely the sha1 +to update to. For security reasons, this feature is not supported +from the `.gitmodules` file. + If the submodule is not yet initialized, and you just want to use the setting as stored in .gitmodules, you can automatically initialize the diff --git a/Documentation/gitmodules.txt b/Documentation/gitmodules.txt index f6c0dfd..f11e872 100644 --- a/Documentation/gitmodules.txt +++ b/Documentation/gitmodules.txt @@ -47,9 +47,14 @@ submodule..update:: in the submodule. If 'none', the submodule with name `$name` will not be updated by default. - - This config option is overridden if 'git submodule update' is given - the '--merge', '--rebase' or '--checkout' options. ++ +This config option is overridden if 'git submodule update' is given +the '--merge', '--rebase' or '--checkout' options. ++ +Only the values 'checkout', 'rebase', 'merge' and 'none' are +recognized when this key appears in the `.gitmodules` file. In +particular, '!command' is not recognised, and will be rewritten to +'none' by "git submodule init". submodule..branch:: A remote branch name for tracking updates in the upstream submodule. -- 2.1.4 ``` ## Junio C Hamano, 2015-03-17 20:49 Subject: Re: git submodule: update=!command Message-ID: URL: https://gitlist.dev/e/xmqqy4mvmjs9.fsf%40gitster.dls.corp.google.com In-Reply-To: <1426620537.1785877.241673949.72FB3B40@webmail.messagingengine.com> ``` Ryan Lortie writes: > 'man git-submodule' contains mention (in one place) that: > > Setting the key submodule.$name.update to !command > will cause command to be run. > > This is not documented in 'man gitmodules' (which documents the other > possible values for the 'update' key) Yes, that is deliberate, because you cannot use !command in .gitmodules that is tracked for security reasons. With more recent versions of Git, namely, the versions after 30a52c1d (Merge branch 'ms/submodule-update-config-doc' into maint, 2015-03-13), the documentation pages already have updated descriptions around this area. ``` ## Ryan Lortie, 2015-03-17 20:59 Subject: Re: git submodule: update=!command Message-ID: <1426625989.1809668.241718517.07249CD6@webmail.messagingengine.com> URL: https://gitlist.dev/e/1426625989.1809668.241718517.07249CD6%40webmail.messagingengine.com In-Reply-To: ``` On Tue, Mar 17, 2015, at 16:49, Junio C Hamano wrote: > With more recent versions of Git, namely, the versions after > 30a52c1d (Merge branch 'ms/submodule-update-config-doc' into maint, > 2015-03-13), the documentation pages already have updated > descriptions around this area. sigh. That's what I get for forgetting to type 'git pull' before writing a patch. Sorry for the noise! Cheers ``` ## Junio C Hamano, 2015-03-17 21:05 Subject: Re: git submodule: update=!command Message-ID: URL: https://gitlist.dev/e/xmqqtwxjmj21.fsf%40gitster.dls.corp.google.com In-Reply-To: <1426625989.1809668.241718517.07249CD6@webmail.messagingengine.com> ``` Ryan Lortie writes: > On Tue, Mar 17, 2015, at 16:49, Junio C Hamano wrote: >> With more recent versions of Git, namely, the versions after >> 30a52c1d (Merge branch 'ms/submodule-update-config-doc' into maint, >> 2015-03-13), the documentation pages already have updated >> descriptions around this area. > > sigh. > > That's what I get for forgetting to type 'git pull' before writing a > patch. > > Sorry for the noise! Nothing to apologise or sigh about. You re-confirmed that the old documentation was lacking, which led to an earlier discussion which in turn led to Michal to update the documentation. If you check the output from git diff 30a52c1d^ 30a52c1d and find it appropriately address the problem you originally had, that would be wonderful, and if you can suggest further improvement, that is equally good. Thanks for participating in our effort to collectively make Git better. ``` ## Ryan Lortie, 2015-03-17 21:11 Subject: Re: git submodule: update=!command Message-ID: <1426626701.1812977.241723449.1C0F64BD@webmail.messagingengine.com> URL: https://gitlist.dev/e/1426626701.1812977.241723449.1C0F64BD%40webmail.messagingengine.com In-Reply-To: ``` kara, On Tue, Mar 17, 2015, at 17:05, Junio C Hamano wrote: > If you check the output from > > git diff 30a52c1d^ 30a52c1d > > and find it appropriately address the problem you originally had, > that would be wonderful, and if you can suggest further improvement, > that is equally good. Indeed, the new version of the docs looks much better. I'm particularly happy about the change to the format to make it easier to visually scan for the possible update modes. Cheers ``` ## Chris Packham, 2015-03-18 07:38 Subject: Re: git submodule: update=!command Message-ID: URL: https://gitlist.dev/e/CAFOYHZA%3Dd94swSvfrR0%2BRdfVrf8a5RwwnYPphtnKz44O_nFeCg%40mail.gmail.com In-Reply-To: <20150317195030.GA18725@peff.net> ``` A little late to this thread On Wed, Mar 18, 2015 at 8:50 AM, Jeff King wrote: > On Tue, Mar 17, 2015 at 03:28:57PM -0400, Ryan Lortie wrote: > >> The first is a question about git's basic policy with respect to things >> like this. I hope that it's safe to assume that running 'git' commands >> on repositories downloaded from potentially-hostile places will never >> result in the authors of those repositories being able to run code on my >> machine. > > Definitely, our policy is that downloading a git repository should not > result in arbitrary code being run. If there is a case of that, it would > be a serious security bug. > > I am not an expert on submodules, but I think the security module there > is: > > 1. You can do whatever you like in submodule.*.update entries in > .git/config, including arbitrary code. Nobody but the user can > write to it. Which was always the intention of the !command feature. It's for users who want to use additional git porcelains that need some help dealing with submodule updates (e.g stgit). > 2. The submodule code may migrate entries from .gitmodules into > .git/config, but does so with an allow-known-good whitelist (see > git-submodule.sh lines 622-637). > > So AFAICT there's no bug here, and the system is working as designed. > It might be worth mentioning that restriction in the submodule > documentation, if only to prevent non-malicious people from wondering > why adding "!foo" does not work in .gitmodules. At the time the !command feature and copying of update config from .gitmodules slid past each other on the list. But out of that I think we got a much better handling that provides security and version compatibility. >> If that is true then, the second request would be to spell this out more >> explicitly in the relevant documentation. I'm happy to write a patch to >> do that, if it is deemed appropriate. > > Yeah, spelling out the security model more explicitly would be good. > There is also some subtlety around hooks. Doing: > > git clone user@host:/path/to/repo.git local > > should never run code controlled by "repo.git" as "user@host". But > doing: > > ssh user@host 'cd /path/to/repo.git && git log' > > will respect the .git/config in repo.git, which may include arbitrary > commands. > > -Peff ``` ## Chris Packham, 2015-03-18 07:43 Subject: Re: git submodule: update=!command Message-ID: URL: https://gitlist.dev/e/CAFOYHZC2Af80EgNgnd7a_DyYnaivthA6vnDEdknQ4ebQfgdGmA%40mail.gmail.com In-Reply-To: ``` On Wed, Mar 18, 2015 at 10:05 AM, Junio C Hamano wrote: > Ryan Lortie writes: > >> On Tue, Mar 17, 2015, at 16:49, Junio C Hamano wrote: >>> With more recent versions of Git, namely, the versions after >>> 30a52c1d (Merge branch 'ms/submodule-update-config-doc' into maint, >>> 2015-03-13), the documentation pages already have updated >>> descriptions around this area. >> >> sigh. >> >> That's what I get for forgetting to type 'git pull' before writing a >> patch. >> >> Sorry for the noise! > > Nothing to apologise or sigh about. You re-confirmed that the old > documentation was lacking, which led to an earlier discussion which > in turn led to Michal to update the documentation. If you check the > output from > > git diff 30a52c1d^ 30a52c1d > > and find it appropriately address the problem you originally had, > that would be wonderful, and if you can suggest further improvement, > that is equally good. I think 30a52c1d could be improved with the following snippet from Ryans patch. "For security reasons, this feature is not supported from the `.gitmodules` file" Or something along those lines. ``` ## Chris Packham, 2015-03-18 07:45 Subject: Re: git submodule: update=!command Message-ID: URL: https://gitlist.dev/e/CAFOYHZBAZ%2BOy-tFDGuiUmA7JcwPG%3DLPPkmX%3DZ%3DRpg4gV%2BcXFMg%40mail.gmail.com In-Reply-To: ``` On Wed, Mar 18, 2015 at 8:43 PM, Chris Packham wrote: > On Wed, Mar 18, 2015 at 10:05 AM, Junio C Hamano wrote: >> Ryan Lortie writes: >> >>> On Tue, Mar 17, 2015, at 16:49, Junio C Hamano wrote: >>>> With more recent versions of Git, namely, the versions after >>>> 30a52c1d (Merge branch 'ms/submodule-update-config-doc' into maint, >>>> 2015-03-13), the documentation pages already have updated >>>> descriptions around this area. >>> >>> sigh. >>> >>> That's what I get for forgetting to type 'git pull' before writing a >>> patch. >>> >>> Sorry for the noise! >> >> Nothing to apologise or sigh about. You re-confirmed that the old >> documentation was lacking, which led to an earlier discussion which >> in turn led to Michal to update the documentation. If you check the >> output from >> >> git diff 30a52c1d^ 30a52c1d >> >> and find it appropriately address the problem you originally had, >> that would be wonderful, and if you can suggest further improvement, >> that is equally good. > > I think 30a52c1d could be improved with the following snippet from Ryans patch. > > "For security reasons, this feature is not supported from the > `.gitmodules` file" > > Or something along those lines. Which is actually down the bottom if I take the time to read the whole diff. ```