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Date: Thu, 20 Mar 2008 08:29:03 -0700 (PDT)
From: Casey Schaufler <casey@...aufler-ca.com>
To: "Serge E. Hallyn" <serue@...ibm.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "Serge E. Hallyn" <serue@...ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
morgan@...nel.org, buraphalinuxserver@...il.com,
lcapitulino@...driva.com.br
Subject: Re: [PATCH 1/1] file capabilities: remove cap_task_kill() (-git)
--- "Serge E. Hallyn" <serue@...ibm.com> wrote:
> Quoting Linus Torvalds (torvalds@...ux-foundation.org):
> >
> >
> > On Wed, 19 Mar 2008, Andrew Morton wrote:
> > >
> > > umm,
> > >
> > > security/smack/smack_lsm.c: In function 'smack_task_kill':
> > > security/smack/smack_lsm.c:1122: error: implicit declaration of function
> 'cap_task_kill'
>
> Right, that was against
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
> which doesn't yet have smack. I should've been clear about that.
>
> > Serge, can you resend with that fixed and the tested-by added?
> >
> > Linus
>
> Following is the version against this morning's mmotm with the tested-by
> added.
>
> thanks,
> -serge
>
>
> >From c50b1c9f7a9e9434c8ddb50cb81e6b342638b8e0 Mon Sep 17 00:00:00 2001
> From: Serge Hallyn <serge@...lyn.com>
> Date: Fri, 29 Feb 2008 15:14:57 +0000
> Subject: [PATCH 1/1] file capabilities: remove cap_task_kill() (-mmotm)
>
> The original justification for cap_task_kill() was as follows:
>
> check_kill_permission() does appropriate uid equivalence checks.
> However with file capabilities it becomes possible for an
> unprivileged user to execute a file with file capabilities
> resulting in a more privileged task with the same uid.
>
> However now that cap_task_kill() always returns 0 (permission
> granted) when p->uid==current->uid, the whole hook is worthless,
> and only likely to create more subtle problems in the corner cases
> where it might still be called but return -EPERM. Those cases
> are basically when uids are different but euid/suid is equivalent
> as per the check in check_kill_permission().
>
> One example of a still-broken application is 'at' for non-root users.
>
> This patch removes cap_task_kill().
>
> Signed-off-by: Serge Hallyn <serge@...lyn.com>
> Acked-by: Andrew G. Morgan <morgan@...nel.org>
> Tested-by: Luiz Fernando N. Capitulino <lcapitulino@...driva.com.br>
Acked-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
> include/linux/security.h | 3 +--
> security/capability.c | 1 -
> security/commoncap.c | 33 ---------------------------------
> security/smack/smack_lsm.c | 5 -----
> 4 files changed, 1 insertions(+), 41 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 2231526..13fd76a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -59,7 +59,6 @@ extern int cap_inode_need_killpriv(struct dentry *dentry);
> extern int cap_inode_killpriv(struct dentry *dentry);
> extern int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t
> old_suid, int flags);
> extern void cap_task_reparent_to_init (struct task_struct *p);
> -extern int cap_task_kill(struct task_struct *p, struct siginfo *info, int
> sig, u32 secid);
> extern int cap_task_prctl(int option, unsigned long arg2, unsigned long
> arg3,
> unsigned long arg4, unsigned long arg5, long *rc_p);
> extern int cap_task_setscheduler (struct task_struct *p, int policy, struct
> sched_param *lp);
> @@ -2276,7 +2275,7 @@ static inline int security_task_kill (struct
> task_struct *p,
> struct siginfo *info, int sig,
> u32 secid)
> {
> - return cap_task_kill(p, info, sig, secid);
> + return 0;
> }
>
> static inline int security_task_wait (struct task_struct *p)
> diff --git a/security/capability.c b/security/capability.c
> index 8340655..38ac54e 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -40,7 +40,6 @@ static struct security_operations capability_ops = {
> .inode_need_killpriv = cap_inode_need_killpriv,
> .inode_killpriv = cap_inode_killpriv,
>
> - .task_kill = cap_task_kill,
> .task_setscheduler = cap_task_setscheduler,
> .task_setioprio = cap_task_setioprio,
> .task_setnice = cap_task_setnice,
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 200361d..e8c3f5e 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -537,34 +537,6 @@ int cap_task_setnice (struct task_struct *p, int nice)
> return cap_safe_nice(p);
> }
>
> -int cap_task_kill(struct task_struct *p, struct siginfo *info,
> - int sig, u32 secid)
> -{
> - /*
> - * Running a setuid root program raises your capabilities.
> - * Killing your own setuid root processes was previously
> - * allowed.
> - * We must preserve legacy signal behavior in this case.
> - */
> - if (p->uid == current->uid)
> - return 0;
> -
> - if (secid)
> - /*
> - * Signal sent as a particular user.
> - * Capabilities are ignored. May be wrong, but it's the
> - * only thing we can do at the moment.
> - * Used only by usb drivers?
> - */
> - return 0;
> - if (cap_issubset(p->cap_permitted, current->cap_permitted))
> - return 0;
> - if (capable(CAP_KILL))
> - return 0;
> -
> - return -EPERM;
> -}
> -
> /*
> * called from kernel/sys.c for prctl(PR_CABSET_DROP)
> * done without task_capability_lock() because it introduces
> @@ -596,11 +568,6 @@ int cap_task_setnice (struct task_struct *p, int nice)
> {
> return 0;
> }
> -int cap_task_kill(struct task_struct *p, struct siginfo *info,
> - int sig, u32 secid)
> -{
> - return 0;
> -}
> #endif
>
> int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 4365fad..2a5eb83 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -1117,11 +1117,6 @@ static int smack_task_movememory(struct task_struct
> *p)
> static int smack_task_kill(struct task_struct *p, struct siginfo *info,
> int sig, u32 secid)
> {
> - int rc;
> -
> - rc = cap_task_kill(p, info, sig, secid);
> - if (rc != 0)
> - return rc;
> /*
> * Sending a signal requires that the sender
> * can write the receiver.
> --
> 1.5.2.5
>
> --
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>
>
Casey Schaufler
casey@...aufler-ca.com
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