Re: [Qemu-devel] [RFC v2 01/12] chardev: avoid crash if no associated address

[Daniel P . Berrangé]

On Fri, Jun 08, 2018 at 11:52:11AM -0300, Philippe Mathieu-Daudé wrote:
> On 06/01/2018 01:27 PM, Marc-André Lureau wrote:
> > A socket chardev may not have associated address (when adding client
> > fd manually for example). But on disconnect, updating socket filename
> > expects an address and may lead to this crash:
> > 
> >   Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
> >   0x0000555555d8c70c in SocketAddress_to_str (prefix=0x555556043062 
> > "disconnected:", addr=0x0, is_listen=false, is_telnet=false) at 
> > /home/elmarco/src/qq/chardev/char-socket.c:388
> >   388           switch (addr->type) {
> >   (gdb) bt
> >   #0  0x0000555555d8c70c in SocketAddress_to_str (prefix=0x555556043062 
> > "disconnected:", addr=0x0, is_listen=false, is_telnet=false) at 
> > /home/elmarco/src/qq/chardev/char-socket.c:388
> >   #1  0x0000555555d8c8aa in update_disconnected_filename (s=0x555556b1ed00) 
> > at /home/elmarco/src/qq/chardev/char-socket.c:419
> >   #2  0x0000555555d8c959 in tcp_chr_disconnect (chr=0x555556b1ed00) at 
> > /home/elmarco/src/qq/chardev/char-socket.c:438
> >   #3  0x0000555555d8cba1 in tcp_chr_hup (channel=0x555556b75690, 
> > cond=G_IO_HUP, opaque=0x555556b1ed00) at 
> > /home/elmarco/src/qq/chardev/char-socket.c:482
> >   #4  0x0000555555da596e in qio_channel_fd_source_dispatch 
> > (source=0x555556bb68b0, callback=0x555555d8cb58 <tcp_chr_hup>, 
> > user_data=0x555556b1ed00) at /home/elmarco/src/qq/io/channel-watch.c:84
> > 
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> >  chardev/char-socket.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> > index 159e69c3b1..f1b7907798 100644
> > --- a/chardev/char-socket.c
> > +++ b/chardev/char-socket.c
> > @@ -416,8 +416,11 @@ static void update_disconnected_filename(SocketChardev 
> > *s)
> >      Chardev *chr = CHARDEV(s);
> >  
> >      g_free(chr->filename);
> > -    chr->filename = SocketAddress_to_str("disconnected:", s->addr,
> > -                                         s->is_listen, s->is_telnet);
> > +    chr->filename = NULL;
> > +    if (s->addr) {
> 
> Isn't it more robust to add this check in SocketAddress_to_str()?

IMHO that just shifts the problem elsewhere - currently SocketAddress_to_str
is assumed to return non-NULL, or to abort(). Shifting the check means it
can now return NULL, so there's every chance the caller will now reference
the NULL pointer that's returned.

> 
>     static char *SocketAddress_to_str(const char *prefix, SocketAddress
> *addr,
>                                       bool is_listen, bool is_telnet)
>     {
>         if (!addr) {
>             return NULL;
>         }
>         switch (addr->type) {
>             ...
> 
> > +        chr->filename = SocketAddress_to_str("disconnected:", s->addr,
> > +                                             s->is_listen, s->is_telnet);
> > +    }
> >  }
> >  
> >  /* NB may be called even if tcp_chr_connect has not been
> > 
> 

Regards,
Daniel
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