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

[Daniel P . Berrangé]

On Fri, Jun 01, 2018 at 06:27:38PM +0200, 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) {
> +        chr->filename = SocketAddress_to_str("disconnected:", s->addr,
> +                                             s->is_listen, s->is_telnet);
> +    }
>  }

This will mean 'chr->filename' as NULL, which means other code using this
field may get NULL - especially the monitor looks like it will printf()
passing a NULL, which is a crash on some platforms. So I think you need
an else clause that will set it to some dummy value.


Regards,
Daniel
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