Re: [Qemu-devel] [PATCH v2] block/ssh: Avoid segfault if inet_connect doesn't set errno.

[Jeff Cody]

On Wed, Jul 22, 2015 at 02:07:22PM +0100, Richard W.M. Jones wrote:
> On some (but not all) systems:
> 
>   $ qemu-img create -f qcow2 overlay -b ssh://xen/
>   Segmentation fault
> 
> It turns out this happens when inet_connect returns -1 in the
> following code, but errno == 0.
> 
>   s->sock = inet_connect(s->hostport, errp);
>   if (s->sock < 0) {
>       ret = -errno;
>       goto err;
>   }
> 
> In the test case above, no host called "xen" exists, so getaddrinfo fails.
> 
> On Fedora 22, getaddrinfo happens to set errno = ENOENT (although it
> is *not* documented to do that), so it doesn't segfault.
> 
> On RHEL 7, errno is not set by the failing getaddrinfo, so ret =
> -errno = 0, so the caller doesn't know there was an error and
> continues with a half-initialized BDRVSSHState struct, and everything
> goes south from there, eventually resulting in a segfault.
> 
> Fix this by setting ret to -EINVAL.  The real error is saved in the
> Error** errp struct, so it is printed correctly:
> 
>   $ ./qemu-img create -f qcow2 overlay -b ssh://xen/
>   qemu-img: overlay: address resolution failed for xen:22: No address 
> associated with hostname
> 
> Signed-off-by: Richard W.M. Jones <address@hidden>
> Reported-by: Jun Li
> BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1147343
> ---
>  block/ssh.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/ssh.c b/block/ssh.c
> index aebb18c..8d4dc2a 100644
> --- a/block/ssh.c
> +++ b/block/ssh.c
> @@ -563,7 +563,7 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
>      /* Open the socket and connect. */
>      s->sock = inet_connect(s->hostport, errp);
>      if (s->sock < 0) {
> -        ret = -errno;
> +        ret = -EINVAL;

Both nbd and sheepdog handle it in a similar fashion (i.e. not relying
on errno being set on inet_connect failure).  However, both nbd and
sheepdog use -EIO as the error return, and I think that makes more
sense.  What do you think?

>          goto err;
>      }
>  
> -- 
> 2.4.3
>