Messages in this thread | | | Subject | Re: [RFC][PATCH v3] Unprivileged: Disable raising of privileges | From | (Eric W. Biederman) | Date | Thu, 31 Dec 2009 08:48:45 -0800 |
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"Serge E. Hallyn" <serue@us.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
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