Re: [PATCH 1/1] file capabilities: remove cap_task_kill()

["BuraphaLinux Server" <buraphalinuxserver@gmail.com>]

For 2.6.25-rc3,
Tested-By: John Gatewood Ham <buraphalinuxserver@gmail.com>

This fixes the 'at' command for non-root users.  Thank you.


On 2/29/08, serge@hallyn.com <serge@hallyn.com> wrote:
> 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@hallyn.com>
> ---
>  include/linux/security.h   |    3 +--
>  security/capability.c      |    1 -
>  security/commoncap.c       |   40 ----------------------------------------
>  security/smack/smack_lsm.c |    5 -----
>  4 files changed, 1 insertions(+), 48 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index fe52cde..95cb830 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -63,7 +63,6 @@ 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);
> @@ -2138,7 +2137,7 @@ 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 bb0c095..06d5c94 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -540,41 +540,6 @@ 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->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;
> -}
> -
>  /*
>   * called from kernel/sys.c for prctl(PR_CABSET_DROP)
>   * done without task_capability_lock() because it introduces
> @@ -605,11 +570,6 @@ 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)
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 770eb06..a9ca412 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -1124,11 +1124,6 @@ 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;
>  	/*
>  	 * Special cases where signals really ought to go through
>  	 * in spite of policy. Stephen Smalley suggests it may
> --
> 1.5.2.5
>
>