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

[Qemu-devel] [PATCH] 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 NULL in the
following code, but errno is not set (0).

  s->sock = inet_connect(s->hostport, errp);
  if (s->sock < 0) {
      ret = -errno;
      goto err;
  }

In the case above, 'xen' doesn't exist 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 == 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.

Fix this by setting errno 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

BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1147343
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 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] block/ssh: Avoid segfault if inet_connect doesn't set errno.

[Richard W.M. Jones]

On Wed, Jul 22, 2015 at 01:07:53PM +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 NULL in the
> following code, but errno is not set (0).

Bleah .. not NULL, -1.  I'm going to send an updated v2
patch which will just fix the message.

Rich.

>   s->sock = inet_connect(s->hostport, errp);
>   if (s->sock < 0) {
>       ret = -errno;
>       goto err;
>   }
> 
> In the case above, 'xen' doesn't exist 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 == 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.
> 
> Fix this by setting errno 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
> 
> BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1147343
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  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
> 

-- 
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