[CVE-2012-2123] lucid/natty fcaps: clear the same personality flags as suid when fcaps are used

[Serge Hallyn]

Quoting Steve Conklin (sconklin at canonical.com):
> This is a clean application of an upstream patch. The same fix has
> already come from upstream stable for Oneiric and Precise.
> 
> -Steve
> 
> From c825bb675aea46fe858b58d1d31dccc6bb7c03c1 Mon Sep 17 00:00:00 2001
> From: Eric Paris <eparis at redhat.com>
> Date: Tue, 17 Apr 2012 16:26:54 -0400
> Subject: [PATCH] fcaps: clear the same personality flags as suid when fcaps
>  are used
> 
> CVE-2012-2123
> 
> BugLink: http://bugs.launchpad.net/bugs/987571
> 
> If a process increases permissions using fcaps all of the dangerous
> personality flags which are cleared for suid apps should also be cleared.
> Thus programs given priviledge with fcaps will continue to have address
> space
> randomization enabled even if the parent tried to disable it to make it
> easier to attack.
> 
> Signed-off-by: Eric Paris <eparis at redhat.com>
> Reviewed-by: Serge Hallyn <serge.hallyn at canonical.com>
> Signed-off-by: James Morris <james.l.morris at oracle.com>
> 
> (cherry picked from commit d52fc5dde1)
> Signed-off-by: Steve Conklin <sconklin at canonical.com>
> ---
>  security/commoncap.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 50be79b..5d5f64b 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -512,6 +512,11 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
>  	}
>  skip:
> 
> +	/* if we have fs caps, clear dangerous personality flags */
> +	if (!cap_issubset(new->cap_permitted, old->cap_permitted))
> +		bprm->per_clear |= PER_CLEAR_ON_SETID;

Don't forget this also needed a follow-up patch to #include
<linux/personality.h>.  (upstream commit
51b79bee627d526199b2f6a6bef8ee0c0739b6d1)

> +
> +
>  	/* Don't let someone trace a set[ug]id/setpcap binary with the revised
>  	 * credentials unless they have the appropriate permit
>  	 */
> -- 
> 1.7.9.5
> 
> -- 
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