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

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

[Richard W.M. Jones]

v2:

I fixed several mistakes in the commit message.  The code change
is the same as before.

Rich.

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

[Richard W.M. Jones]

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 <rjones@redhat.com>
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;
         goto err;
     }
 
-- 
2.4.3

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

[Daniel P. Berrange]

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 <rjones@redhat.com>
> 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;
>          goto err;

There are a reasonable number of other uses of inet_connect() in QEMU,
so can't we fix inet_connect() itself to set EINVAL in the error case
instead of just fixing one caller.


Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

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

[Richard W.M. Jones]

On Wed, Jul 22, 2015 at 02:10:51PM +0100, Daniel P. Berrange wrote:
> There are a reasonable number of other uses of inet_connect() in QEMU,
> so can't we fix inet_connect() itself to set EINVAL in the error case
> instead of just fixing one caller.

The only users I can find are block/nbd.c and block/sheepdog.c, and
neither of those is expecting errno to be set.  So I think my use of
errno in block/ssh.c was flat out wrong, although it happened to work
most of the time.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top

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

[Kevin Wolf]

Am 22.07.2015 um 15:10 hat Daniel P. Berrange geschrieben:
> 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 <rjones@redhat.com>
> > 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;
> >          goto err;
> 
> There are a reasonable number of other uses of inet_connect() in QEMU,
> so can't we fix inet_connect() itself to set EINVAL in the error case
> instead of just fixing one caller.

None of the other callers try to use errno, which isn't even documented
as part of the inet_connect() interface. So I think setting errno inside
inet_connect() would be wrong.

If we were to change anything, we might consider returning -EINVAL
instead of -1, though I'm not sure how useful that change would be. We
would still have to fix this call in the ssh block driver.

Kevin

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 <rjones@redhat.com>
> 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
> 

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

[Richard W.M. Jones]

On Wed, Jul 22, 2015 at 09:17:49AM -0400, Jeff Cody wrote:
> 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?

If you prefer -- I don't mind as long as it doesn't segfault :-)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

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

[Jeff Cody]

On Wed, Jul 22, 2015 at 02:22:18PM +0100, Richard W.M. Jones wrote:
> On Wed, Jul 22, 2015 at 09:17:49AM -0400, Jeff Cody wrote:
> > 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?
> 
> If you prefer -- I don't mind as long as it doesn't segfault :-)
>

I think I would - mainly for consistency, but also because -EIO better
describes all the various failures that may occur in inet_connect().

Thanks!
Jeff