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Date: Thu, 31 Dec 2009 08:48:45 -0800 From: ebiederm@...ssion.com (Eric W. Biederman) To: "Serge E. Hallyn" <serue@...ibm.com> Cc: "Andrew G. Morgan" <morgan@...nel.org>, Bryan Donlan <bdonlan@...il.com>, Alan Cox <alan@...rguk.ukuu.org.uk>, Benny Amorsen <benny+usenet@...rsen.dk>, Michael Stone <michael@...top.org>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, linux-security-module@...r.kernel.org, Andi Kleen <andi@...stfloor.org>, David Lang <david@...g.hm>, Oliver Hartkopp <socketcan@...tkopp.net>, Herbert Xu <herbert@...dor.apana.org.au>, Valdis Kletnieks <Valdis.Kletnieks@...edu>, Evgeniy Polyakov <zbr@...emap.net>, "C. Scott Ananian" <cscott@...ott.net>, James Morris <jmorris@...ei.org>, Bernie Innocenti <bernie@...ewiz.org>, Mark Seaborn <mrs@...hic-beasts.com>, Randy Dunlap <randy.dunlap@...cle.com>, Américo Wang <xiyou.wangcong@...il.com>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Samir Bellabes <sam@...ack.fr>, Casey Schaufler <casey@...aufler-ca.com>, Pavel Machek <pavel@....cz>, Al Viro <viro@...iv.linux.org.uk> Subject: Re: [RFC][PATCH v3] Unprivileged: Disable raising of privileges "Serge E. Hallyn" <serue@...ibm.com> writes: >> diff --git a/security/commoncap.c b/security/commoncap.c >> index f800fdb..34500e3 100644 >> --- a/security/commoncap.c >> +++ b/security/commoncap.c >> @@ -389,7 +389,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective) >> if (!file_caps_enabled) >> return 0; >> >> - if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID) >> + if (bprm->nosuid) >> return 0; > > I'm sorry, this may actually not be sufficient. > > Could you try the following test on a kernel with this patch? : > > 1. become root > 2. do prctl(PR_SET_NOSUID); > 3. run bash, and examine your capabilities in /proc/self/status > > I think the code in security/commoncap.c:457-458 will re-raise your > capabilities. Right. That is a legitimate issue. I almost guard against it with my test against with my start condition test of cap_isclear(cred->cap_permitted). Which causes this to fail for root in most situations. I will add a test for the securebits, and deny this to root unless the securebits are such that root cannot gain privilege. Thanks for catching this. I figured I might need a uid == 0 exclusion. Where the test was split when I wrote it I wasn't certain where to put it. Eric -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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