[Spice-devel] [PATCH vd_agent_win] Use sprintf_s instead of sprintf to not crash

[Frediano Ziglio]

> 
> On Wed, May 17, 2017 at 12:57:34PM -0400, Frediano Ziglio wrote:
> > > 
> > > > 
> > > > ---
> > > >  vdagent/file_xfer.cpp | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/vdagent/file_xfer.cpp b/vdagent/file_xfer.cpp
> > > > index de1aea1..de98d50 100644
> > > > --- a/vdagent/file_xfer.cpp
> > > > +++ b/vdagent/file_xfer.cpp
> > > > @@ -113,8 +113,8 @@ void
> > > > FileXfer::handle_start(VDAgentFileXferStartMessage*
> > > > start,
> > > >          if (attempt == 0) {
> > > >              strcpy(dest_filename, file_name);
> > > >          } else {
> > > > -            sprintf(dest_filename, "%.*s (%d)%s", int(extension -
> > > > file_name), file_name,
> > > > -                    attempt, extension);
> > > > +            sprintf_s(dest_filename, SPICE_N_ELEMENTS(file_name) +
> > > > POSTFIX_LEN,
> > > > +                      "%.*s (%d)%s", int(extension - file_name),
> > > > file_name,
> > > > attempt, extension);
> > > >          }
> > > >          if ((MultiByteToWideChar(CP_UTF8, 0, dest_filename, -1,
> > > >          file_path
> > > >          +
> > > >          wlen, MAX_PATH - wlen)) == 0) {
> > > >              vd_printf("failed converting file_name:%s to WideChar",
> > > >              dest_filename);
> > > 
> > > As far as I know dest_filename is allocate big enough to avoid the
> > > overflow.
> > > Did it crash for you or just a warning from the compiler?
> > > 
> > > This would be easier
> > > 
> > >             sprintf_s(dest_filename, SPICE_N_ELEMENTS(dest_filename),
> > >                       "%.*s (%d)%s", int(extension - file_name),
> > >                       file_name,
> > >                       attempt, extension);
> > > 
> > > without computing again the length.
> > > 
> > 
> > Got some discussion with Jakub and Pavel on IRC.
> > They confirmed that with Fedora 26 and 27 the crash happens.
> > I tried to do some tests (removed the CreateFile and some calls to have
> > a test function) with Fedora 25 but didn't manage to reproduce.
> > Jakub reported that this happens with small names.
> > 
> > Maybe is an issue with MingW with newer Fedora? Worth investigating.
> 
> This is pushed already, but this should have been added to the commit
> log.
> 
> Christophe
> 

I think would be better to open a bug trying to understand where the problem
is. The source should not crash with old code.
I spent last 2 hours trying to compile the agent using mock (my machine
is using Fedora 25) but not managed so far.
I was trying to write a patch to build a test case but with Fedora 25
and Wine the test case works correctly.

Frediano