Re: [Qemu-devel] [PATCH v2] slirp: use less predictable directory name in /tmp for smb config (CVE-2015-4037)

[Miroslav Rezanina <mrezanin@redhat.com>]

On Tue, Jun 02, 2015 at 08:46:35AM +0300, Michael Tokarev wrote:
> In this version I used mkdtemp(3) which is:
> 
>         _BSD_SOURCE
>         || /* Since glibc 2.10: */
>             (_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
> 
> (POSIX.1-2008), so should be available on systems we care about.
> 
> While at it, reset the resulting directory name within smb structure
> on error so cleanup function wont try to remove directory which we
> failed to create.
> 
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
> v2:
> Add resetting of the dirname on failure so that cleanup function
> does not try to remove directory which we failed to create.
> 
> Use snprintf() as was in the original code, not strcpy(): while
> in this very case it does not matter at all since both strings
> are of known size, some people dislike strcpy() in principle.
> 
>  net/slirp.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/net/slirp.c b/net/slirp.c
> index 0e15cf6..3533837 100644
> --- a/net/slirp.c
> +++ b/net/slirp.c
> @@ -481,7 +481,6 @@ static void slirp_smb_cleanup(SlirpState *s)
>  static int slirp_smb(SlirpState* s, const char *exported_dir,
>                       struct in_addr vserver_addr)
>  {
> -    static int instance;
>      char smb_conf[128];
>      char smb_cmdline[128];
>      struct passwd *passwd;
> @@ -505,10 +504,10 @@ static int slirp_smb(SlirpState* s, const char *exported_dir,
>          return -1;
>      }
>  
> -    snprintf(s->smb_dir, sizeof(s->smb_dir), "/tmp/qemu-smb.%ld-%d",
> -             (long)getpid(), instance++);
> -    if (mkdir(s->smb_dir, 0700) < 0) {
> +    snprintf(s->smb_dir, sizeof(s->smb_dir), "/tmp/qemu-smb.XXXXXX");
> +    if (!mkdtemp(s->smb_dir)) {
>          error_report("could not create samba server dir '%s'", s->smb_dir);
> +        s->smb_dir[0] = 0;
>          return -1;
>      }
>      snprintf(smb_conf, sizeof(smb_conf), "%s/%s", s->smb_dir, "smb.conf");
> -- 
> 2.1.4
> 
> 
Reviewed-by: Miroslav Rezanina <mrezanin@redhat.com>