Re: [PATCH] daemon: sanitize all directory separators

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mar 26, 2021, 14:47 UTC
Message-ID: <nycvar.QRO.7.76.6.2103261543550.52@tvgsbejvaqbjf.bet>
In-Reply-To: <xmqq5z1fuen6.fsf@gitster.g>

Hi Junio & René,

On Thu, 25 Mar 2021, Junio C Hamano wrote:

Show 12 quoted lines

> René Scharfe. <l.s.r@web.de> writes:
>
> > When sanitizing client-supplied strings on Windows, also strip off
> > backslashes, not just slashes.
> >
> > Signed-off-by: René Scharfe <l.s.r@web.de>
> > ---
> >  daemon.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
>
> I do not know how common is it to run "git daemon" on Windows, but
> it would be nice to have at least an ack from Windows person.

Here is my ACK.

I do not have any precise numbers, of course, as we do not have any telemetry in Git for Windows (for better or worse).

There _are_ occasional reports about something in `git daemon` not working; Most notably, you have to turn off the sideband to make `push` work.

Show 18 quoted lines

> > diff --git a/daemon.c b/daemon.c
> > index 2ab7ea82eb..0561c19ee8 100644
> > --- a/daemon.c
> > +++ b/daemon.c
> > @@ -566,14 +566,14 @@ static void parse_host_and_port(char *hostport, char **host,
> >
> >  /*
> >   * Sanitize a string from the client so that it's OK to be inserted into a
> > - * filesystem path. Specifically, we disallow slashes, runs of "..", and
> > - * trailing and leading dots, which means that the client cannot escape
> > - * our base path via ".." traversal.
> > + * filesystem path. Specifically, we disallow directory separators, runs
> > + * of "..", and trailing and leading dots, which means that the client
> > + * cannot escape our base path via ".." traversal.
>
> Not a new problem, but "runs of '..'" confused me.  If I am reading
> the code right, we disallow directory separators (by ignoring) and
> two or more '.' in a row (by squashing them into a single '.').

Indeed, the code is a bit funny in that respect. But at least it keeps us somewhat safe: there is currently no way to break out of the directory to the parent directory, whether with this path or not. (Phew!)

Thanks, Dscho

Show 15 quoted lines

>
> >   */
> >  static void sanitize_client(struct strbuf *out, const char *in)
> >  {
> >  	for (; *in; in++) {
> > -		if (*in == '/')
> > +		if (is_dir_sep(*in))
> >  			continue;
> >  		if (*in == '.' && (!out->len || out->buf[out->len - 1] == '.'))
> >  			continue;
> > --
> > 2.30.2
>
> Thanks.
>