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

[Serge E. Hallyn]

Quoting BuraphaLinux Server (buraphalinuxserver@xxxxxxxxx):
> For 2.6.25-rc3,
> Tested-By: John Gatewood Ham <buraphalinuxserver@xxxxxxxxx>
> 
> This fixes the 'at' command for non-root users.  Thank you.

Cool, thanks much for testing.

-serge

> On 2/29/08, serge@xxxxxxxxxx <serge@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  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
> >
> >
> --
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