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

[Markus Armbruster]

Michael Tokarev <address@hidden> writes:

> In this version I used mkdtemp(3) which is:
>
>         _BSD_SOURCE
>         || /* Since glibc 2.10: */
>             (_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
>
> so should be available on systems we care about.
>
> Signed-off-by: Michael Tokarev <address@hidden>
> ---
>  net/slirp.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/slirp.c b/net/slirp.c
> index 9bbed74..0ad32ad 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;
> @@ -505,9 +504,8 @@ 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) {
> +    strcpy(s->smb_dir, "/tmp/qemu-smb.XXXXXX");
> +    if (!mkdtemp(s->smb_dir)) {
>          error_report("could not create samba server dir '%s'", s->smb_dir);
>          return -1;
>      }

Uh, I have to suspend my R-by.  This clobbers s->smb_dir[] when
mkdtemp() fails.  Is that safe?  Explain why, and get my R-by back.

The alternative "[PATCH] net: fix insecure temporary file creation in
SLiRP" doesn't clobber it.
http://lists.nongnu.org/archive/html/qemu-devel/2015-06/msg00005.html