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Date: Wed, 5 Mar 2008 20:17:11 +0100
From: Chris Friedhoff <chris@...edhoff.org>
To: linux-security-module@...r.kernel.org
Cc: chris@...edhoff.org, serge@...lyn.com,
lkml <linux-kernel@...r.kernel.org>,
linux-security-module@...r.kernel.org,
Andrew Morgan <morgan@...nel.org>,
Stephen Smalley <sds@...ch.ncsc.mil>,
Mike Galbraith <efault@....de>, buraphalinuxserver@...il.com,
elendil@...net.nl, stable@...nel.org
Subject: Re: [PATCH 1/1] file capabilities: remove cap_task_kill()
It works here against 2.6.24.3.
Originaly it was a fix - if I recall correctly - to allow a self
started X to kill completly. This works with the patch.
Chris
On Fri, 29 Feb 2008 15:26:34 -0600
serge@...lyn.com wrote:
> Quoting Luiz Fernando N. Capitulino (lcapitulino@...driva.com.br):
> > Em Thu, 28 Feb 2008 11:38:17 -0600
> > serge@...lyn.com escreveu:
> >
> > | 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().
> > |
> > | This patch removes cap_task_kill().
> >
> > 2.6.24 seems to have the same bug, what about a rediff for it and
> > submit the patch to -stable team?
>
> Luiz, could you confirm that the below works?
>
> thanks,
> -serge
>
> From c77b7d418933c14707383f06a1da61169e84071b 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()
>
> 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().
>
> This patch removes cap_task_kill().
>
> Signed-off-by: Serge Hallyn <serge@...lyn.com>
> ---
> include/linux/security.h | 3 +--
> security/capability.c | 1 -
> security/commoncap.c | 39 ---------------------------------------
> 3 files changed, 1 insertions(+), 42 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index ac05083..d842ee3 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -62,7 +62,6 @@ 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_setscheduler (struct task_struct *p, int policy, struct sched_param *lp);
> extern int cap_task_setioprio (struct task_struct *p, int ioprio);
> extern int cap_task_setnice (struct task_struct *p, int nice);
> @@ -2112,7 +2111,7 @@ 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 9e99f36..2c6e06d 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 ea61bc7..6e9065c 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -527,40 +527,6 @@ 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)
> -{
> - if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
> - return 0;
> -
> - /*
> - * 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->euid == 0 && p->uid == current->uid)
> - return 0;
> -
> - /* sigcont is permitted within same session */
> - if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p)))
> - 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;
> -}
> #else
> int cap_task_setscheduler (struct task_struct *p, int policy,
> struct sched_param *lp)
> @@ -575,11 +541,6 @@ 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
>
> void cap_task_reparent_to_init (struct task_struct *p)
> --
> 1.5.2.5
>
> --
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--------------------
Chris Friedhoff
chris@...edhoff.org
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