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Re: [libvirt] [PATCH] rpc: avoid ssh interpreting malicious hostname as arguments



On 08/29/2017 04:14 PM, Daniel P. Berrange wrote:
> Inspired by the recent GIT / Mercurial security flaws
> (http://blog.recurity-labs.com/2017-08-10/scm-vulns),
> consider someone/something manages to feed libvirt a bogus
> URI such as:

Yeah, I was wondering this myself when reading the news on my PTO but
you beat me to it :-)

> 
>   virsh -c qemu+ssh://-oProxyCommand=gnome-calculator/system
> 
> In this case, the hosname "-oProxyCommand=gnome-calculator"
> will get interpreted as an argument to ssh, not a hostname.
> Fortunately, due to the set of args we have following the
> hostname, SSH will then interpret our bit of shell script
> that runs 'nc' on the remote host as a cipher name, which is
> clearly invalid. This makes ssh exit during argv parsing and
> so it never tries to run gnome-calculator.
> 
> We are lucky this time, but lets be more paranoid, by using
> '--' to explicitly tell SSH when it has finished seeing
> command line options. This forces it to interpret
> "-oProxyCommand=gnome-calculator" as a hostname, and thus
> see a fail from hostname lookup.
> 
> Signed-off-by: Daniel P. Berrange <berrange redhat com>
> ---
>  src/rpc/virnetsocket.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/rpc/virnetsocket.c b/src/rpc/virnetsocket.c
> index d228c8a8c..23089afef 100644
> --- a/src/rpc/virnetsocket.c
> +++ b/src/rpc/virnetsocket.c
> @@ -868,7 +868,7 @@ int virNetSocketNewConnectSSH(const char *nodename,
>      if (!netcat)
>          netcat = "nc";
>  
> -    virCommandAddArgList(cmd, nodename, "sh", "-c", NULL);
> +    virCommandAddArgList(cmd, "--", nodename, "sh", "-c", NULL);
>  
>      virBufferEscapeShell(&buf, netcat);
>      if (virBufferCheckError(&buf) < 0) {
> 

ACK and safe for the freeze.

Michal


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