Re: a problem with git describe

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Carlo,

On Mon, 25 Apr 2022, Carlo Marcelo Arenas Belón wrote:

> On Mon, Apr 25, 2022 at 12:02:45AM -0700, Carlo Marcelo Arenas Belón wrote:
> > On Sun, Apr 24, 2022 at 11:39:27PM -0700, Junio C Hamano wrote:
> > > Carlo Marcelo Arenas Belón <carenas@gmail.com> writes:
> > >
> > > > At that point, though you might as well excempt root from this check
> > >
> > > But "root" or any higher-valued account is what needs this kind of
> > > protection the most, no?
> >
> > correct, and I didn't meant to excempt root from the protection, but
> > from the check that requires that the config file ownership matches.
> >
> > if the config file is owned by root, we already lost, regardless of what
> > uid git is running as.
>
> apologies for my confusing english, hopefully this C is clearer
>
> diff --git a/git-compat-util.h b/git-compat-util.h
> index 58fd813bd01..6a385be7d1d 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -440,9 +440,19 @@ static inline int git_offset_1st_component(const char *path)
>  static inline int is_path_owned_by_current_uid(const char *path)
>  {
>  	struct stat st;
> +	uid_t euid;
> +
>  	if (lstat(path, &st))
>  		return 0;
> -	return st.st_uid == geteuid();
> +
> +	euid = geteuid();
> +	if (!euid && st.st_uid && isatty(0)) {
> +		struct stat ttyst;
> +		if (!stat(ttyname(0), &ttyst))
> +			euid = ttyst.st_uid;
> +	}
> +
> +	return st.st_uid == euid;
>  }
>
>  #define is_path_owned_by_current_user is_path_owned_by_current_uid
>
> it uses stdin instead not to fall in the issue that was raised by
> Gábor, but I am affraid that it might need to check all stdnandles for
> a valid tty to be safe, and it looking even more complex.

Maybe a better idea for the `sudo` scenario would be to make use of
`SUDO_UID` (assuming that no adversary can gain control over the user's
environment variables)?

Ciao,
Dscho