From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752958AbZL3OwO (ORCPT ); Wed, 30 Dec 2009 09:52:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752075AbZL3OwM (ORCPT ); Wed, 30 Dec 2009 09:52:12 -0500 Received: from mail-pw0-f42.google.com ([209.85.160.42]:51608 "EHLO mail-pw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751760AbZL3OwL convert rfc822-to-8bit (ORCPT ); Wed, 30 Dec 2009 09:52:11 -0500 MIME-Version: 1.0 In-Reply-To: References: <20091229050114.GC14362@heat> <20091229211139.0732a0c1@lxorguk.ukuu.org.uk> <20091229223631.GB22578@us.ibm.com> <3e8340490912291954v5a837a26p64bd776102d281d7@mail.gmail.com> <3e8340490912292057g3e87eaabn115f85b78af2b08c@mail.gmail.com> Date: Wed, 30 Dec 2009 06:52:08 -0800 X-Google-Sender-Auth: 04fd0b0486bfe24c Message-ID: <551280e50912300652r1007dee0j8de750bf33af9b3c@mail.gmail.com> Subject: Re: [RFC][PATCH v2] Unprivileged: Disable raising of privileges From: "Andrew G. Morgan" To: "Eric W. Biederman" Cc: Bryan Donlan , "Serge E. Hallyn" , Alan Cox , Benny Amorsen , Michael Stone , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-security-module@vger.kernel.org, Andi Kleen , David Lang , Oliver Hartkopp , Herbert Xu , Valdis Kletnieks , Evgeniy Polyakov , "C. Scott Ananian" , James Morris , Bernie Innocenti , Mark Seaborn , Randy Dunlap , =?ISO-8859-1?Q?Am=E9rico_Wang?= , Tetsuo Handa , Samir Bellabes , Casey Schaufler , Pavel Machek , Al Viro Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Eric, I'm not clear why capabilities need to be manipulated by this feature (the pure capability support already has a feature for disabling privilege and blocking unsafe, or insufficient privilege, execution). Perhaps I'm just unclear what features can be more safely enabled with this in effect - that is, your description suggests that this is why you are doing this, but leaves it unclear what they are. Could you take a few moments to enumerate some of them? Thanks Andrew On Wed, Dec 30, 2009 at 4:49 AM, Eric W. Biederman wrote: > > If we can know that a process will never raise > it's priveleges we can enable a lot of features > that otherwise would be unsafe, because they > could break assumptions of existing suid executables. > > To allow this to be used as a sand boxing feature > also disable ptracing other executables without > this new restriction. > > For the moment I have used a per thread flag because > we are out of per process flags. > > To ensure all descendants get this flag I rely on > the default copying of procss structures. > > Added bprm->nosuid to make remove the need to add > duplicate error prone checks.  This ensures that > the disabling of suid executables is exactly the > same as MNT_NOSUID. > > Signed-off-by: Eric W. Biederman > --- >  arch/x86/include/asm/thread_info.h |    2 ++ >  fs/exec.c                          |    6 ++++-- >  include/linux/binfmts.h            |    1 + >  include/linux/prctl.h              |    2 ++ >  kernel/ptrace.c                    |    4 ++++ >  kernel/sys.c                       |   16 ++++++++++++++++ >  security/commoncap.c               |   14 +++++++++++++- >  security/selinux/hooks.c           |    2 +- >  8 files changed, 43 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h > index 375c917..e716203 100644 > --- a/arch/x86/include/asm/thread_info.h > +++ b/arch/x86/include/asm/thread_info.h > @@ -82,6 +82,7 @@ struct thread_info { >  #define TIF_SYSCALL_EMU                6       /* syscall emulation active */ >  #define TIF_SYSCALL_AUDIT      7       /* syscall auditing active */ >  #define TIF_SECCOMP            8       /* secure computing */ > +#define TIF_NOSUID             9       /* suid exec permanently disabled */ >  #define TIF_MCE_NOTIFY         10      /* notify userspace of an MCE */ >  #define TIF_USER_RETURN_NOTIFY 11      /* notify kernel of userspace return */ >  #define TIF_NOTSC              16      /* TSC is not accessible in userland */ > @@ -107,6 +108,7 @@ struct thread_info { >  #define _TIF_SYSCALL_EMU       (1 << TIF_SYSCALL_EMU) >  #define _TIF_SYSCALL_AUDIT     (1 << TIF_SYSCALL_AUDIT) >  #define _TIF_SECCOMP           (1 << TIF_SECCOMP) > +#define _TIF_NOSUID            (1 << TIF_NOSUID) >  #define _TIF_MCE_NOTIFY                (1 << TIF_MCE_NOTIFY) >  #define _TIF_USER_RETURN_NOTIFY        (1 << TIF_USER_RETURN_NOTIFY) >  #define _TIF_NOTSC             (1 << TIF_NOTSC) > diff --git a/fs/exec.c b/fs/exec.c > index 632b02e..5cba5ac 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1131,8 +1131,10 @@ int prepare_binprm(struct linux_binprm *bprm) >        /* clear any previous set[ug]id data from a previous binary */ >        bprm->cred->euid = current_euid(); >        bprm->cred->egid = current_egid(); > - > -       if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) { > +       bprm->nosuid = > +               (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) || > +               test_tsk_thread_flag(current, TIF_NOSUID); > +       if (bprm->nosuid) { >                /* Set-uid? */ >                if (mode & S_ISUID) { >                        bprm->per_clear |= PER_CLEAR_ON_SETID; > diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h > index cd4349b..c3b5a30 100644 > --- a/include/linux/binfmts.h > +++ b/include/linux/binfmts.h > @@ -44,6 +44,7 @@ struct linux_binprm{ >  #ifdef __alpha__ >        unsigned int taso:1; >  #endif > +       unsigned int nosuid:1;  /* True if suid bits are ignored */ >        unsigned int recursion_depth; >        struct file * file; >        struct cred *cred;      /* new credentials */ > diff --git a/include/linux/prctl.h b/include/linux/prctl.h > index a3baeb2..acb3516 100644 > --- a/include/linux/prctl.h > +++ b/include/linux/prctl.h > @@ -102,4 +102,6 @@ > >  #define PR_MCE_KILL_GET 34 > > +#define PR_SET_NOSUID  35 > + >  #endif /* _LINUX_PRCTL_H */ > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index 23bd09c..b91040c 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -152,6 +152,10 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode) >        if (!dumpable && !capable(CAP_SYS_PTRACE)) >                return -EPERM; > > +       if (test_tsk_thread_flag(current, TIF_NOSUID) && > +           !test_tsk_thread_flag(task, TIF_NOSUID)) > +               return -EPERM; > + >        return security_ptrace_access_check(task, mode); >  } > > diff --git a/kernel/sys.c b/kernel/sys.c > index 26a6b73..1d1902a 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1578,6 +1578,22 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, >                        else >                                error = PR_MCE_KILL_DEFAULT; >                        break; > +               case PR_SET_NOSUID: > +               { > +                       const struct cred *cred = current->cred; > +                       error = -EINVAL; > +                       if (    (cred->uid != cred->suid) || > +                               (cred->uid != cred->euid) || > +                               (cred->uid != cred->fsuid) || > +                               (cred->gid != cred->sgid) || > +                               (cred->gid != cred->egid) || > +                               (cred->gid != cred->fsgid) || > +                               (atomic_read(¤t->signal->count) != 1)) > +                               break; > +                       error = 0; > +                       set_tsk_thread_flag(current, TIF_NOSUID); > +                       break; > +               } >                default: >                        error = -EINVAL; >                        break; > diff --git a/security/commoncap.c b/security/commoncap.c > index f800fdb..28ab286 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; > >        dentry = dget(bprm->file->f_dentry); > @@ -869,6 +869,18 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3, >                        new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); >                goto changed; > > +       case PR_SET_NOSUID: > +       { > +               const struct cred *cred = current->cred; > +               error = -EINVAL; > +               /* Perform the capabilities checks */ > +               if (!cap_isclear(cred->cap_permitted) || > +                   !cap_isclear(cred->cap_effective)) > +                       goto error; > +               /* Have the default perform the rest of the work. */ > +               error = -ENOSYS; > +               goto error; > +       } >        default: >                /* No functionality available - continue with default */ >                error = -ENOSYS; > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 7a374c2..d14cd24 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -2147,7 +2147,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm) >        COMMON_AUDIT_DATA_INIT(&ad, FS); >        ad.u.fs.path = bprm->file->f_path; > > -       if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) > +       if (bprm->nosid) >                new_tsec->sid = old_tsec->sid; > >        if (new_tsec->sid == old_tsec->sid) { > -- > 1.6.5.2.143.g8cc62 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at  http://vger.kernel.org/majordomo-info.html >