Re: [PATCH] Sanitize escape char sequences coming from server

[Pavel Cahyna <pcahyna@redhat.com>]

Hello,

On Thu, Jun 21, 2018 at 01:41:22PM -0400, Jeff King wrote:
> On Thu, Jun 21, 2018 at 02:10:30PM +0200, Sebastian Kisela wrote:
> 
> > From: Sebastian Kisela <skisela@redhat.com>
> > +	int len = mbstowcs(wcstring, outbuf->buf, outbuf->len);
> 
> I don't think mbstowcs() is always going to do the right thing there.
> We're looking at a string that was sent from the remote server. What
> encoding is it in? Using mbstowcs() is going to use whatever is in
> LC_CTYPE on the local machine.

Exactly. The point is, everything should continue to work if the local
machine and the server agreed on the encoding. Imagine a
non-English-speaking site where the administrators configured the Git
server to output non-ASCII messages and the clients are configured with
a matching locale which allows the users to see them. We should ensure
everything keeps working in this case.

> > +	for(int i = 0; i <= len; i++)
> > +		if(!isprint(wcstring[i]) && !isspace(wcstring[i]) )
> > +			wcstring[i] = '?';
> > +		if (wcstombs(outbuf->buf, wcstring, outbuf->len) == -1)
> > +			return 1;
> 
> Funny indentation. I think the second line is supposed to _not_ be in
> the loop, so this is just funny indentation and not wrong code.
> 
> Using isprint() here probably doesn't do what you expect, because Git
> uses its own locale-agnostic ctype replacements. I didn't check, but I
> suspect any non-ascii characters will be marked as non-printable, making
> the whole wchar thing pointless.

isw*() was probably intended instead of is*()

> Your replacement allows existing spaces, which is good; many servers
> send carriage-returns as part of progress output (and recv_sideband
> detects these and makes sure the line remains prefixed with "remote:").
> 
> > @@ -74,6 +89,9 @@ int recv_sideband(const char *me, int in_stream, int out)
> >  				} else {
> >  					strbuf_addch(&outbuf, *brk);
> >  				}
> > +
> > +				if (sanitize_server_message(&outbuf))
> > +					retval = SIDEBAND_REMOTE_ERROR;
> 
> "outbuf" may contain partially-received lines at various points, meaning
> multi-byte characters could be cut off. I _think_ it's OK to look at it
> here, as we'd always be breaking on a "\r" or "\n" at this point.

Maybe sanitize_server_message should return a mbstate_t to keep state
between invocations?

Thanks, Pavel