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 Content-Length: 8586 Lines: 210 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/