Quoting Stephen Smalley ([email protected]):
> On Wed, 2007-10-31 at 18:49 -0500, Serge E. Hallyn wrote:
> > >From 5bff8967f45a35f858b96ca673d9bf98eac53d49 Mon Sep 17 00:00:00 2001
> > From: Serge E. Hallyn <[email protected]>
> > Date: Wed, 31 Oct 2007 11:22:04 -0500
> > Subject: [PATCH 1/1] file capabilities: allow sigcont within session (v2)
> >
> > (This is a proposed fix to http://bugzilla.kernel.org/show_bug.cgi?id=9247)
> >
> > Allow sigcont to be sent to a process with greater capabilities
> > if it is in the same session. Otherwise, a shell from which
> > I've started a root shell and done 'suspend' can't be restarted
> > by the parent shell.
> >
> > Also don't do file-capabilities signaling checks when uids for
> > the processes don't match, since the standard check_kill_permission
> > will have done those checks.
>
> Description doesn't match the code.
Egads. I knew I should've just kept that part out of it for the first
patch...
New patch on top of previous one is appended.
Thanks.
> And in the non-matching uid case,
> check_kill_permission typically returns an error before it reaches
> cap_task_kill (modulo the special cases).
Typically, but when it doesn't, then the file capabilities shouldn't get
in the way of check_kill_permission() granting permission. The file
capabilities
>
> >
> > Signed-off-by: Serge E. Hallyn <[email protected]>
> > ---
> > security/commoncap.c | 9 +++++++++
> > 1 files changed, 9 insertions(+), 0 deletions(-)
> >
> > diff --git a/security/commoncap.c b/security/commoncap.c
> > index bf67871..4de6857 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -526,6 +526,15 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
> > if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
> > return 0;
> >
> > + /* if tasks have same uid, then check_kill_permission did check */
> > + if (current->uid == p->uid || current->euid == p->uid ||
> > + current->uid == p->suid || current->euid == p->suid)
> > + return 0;
>
> I'm confused - if you are allowing all signals within the same uid, then
No I was confused. I wanted to allow for tasks with different uids.
But in fact that's not safe anyway. A binary can be setuid and owned by
a non-root user user1, have file capabilities, and be executed by user2.
(Anyway given how grossly my code missed my erroneous intentions, I need
to add some signal tests to my file capabilities tests - and get those
tests into LTP)
> what was the point of having a cap_task_kill at all? cap_task_kill was
> supposed to prevent a process with lesser capabilities from killing a
> process with more capabilities, even if they have the same uid, so that
> when you have a program marked with file capabilities instead of a
> setuid-0 program, that program can't be sent arbitrary signals by the
> caller.
>
> > +
> > + /* 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.
> --
> Stephen Smalley
> National Security Agency
Thanks, Stephen.
>From 98741f07ab1bc4a1fc2de7fedfb9023ea30bf988 Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <[email protected]>
Date: Thu, 1 Nov 2007 08:20:12 -0500
Subject: [PATCH 1/1] file capabilities: remove the non-matching uid special case for kill
There I went again having one patch do two (related) things.
Remove the special check I had added to cap_task_kill() for
non-matching uids. In fact it turns out the check wouldn't be
safe even if I'd coded it correctly. A binary can be setuid
and owned by a non-root user user1, have file capabilities, and
be executed by user2.
Signed-off-by: Serge E. Hallyn <[email protected]>
---
security/commoncap.c | 5 -----
1 files changed, 0 insertions(+), 5 deletions(-)
diff --git a/security/commoncap.c b/security/commoncap.c
index f04784a..302e8d0 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -526,11 +526,6 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
return 0;
- /* if tasks have same uid, then check_kill_permission did check */
- if (current->uid == p->uid || current->euid == p->uid ||
- current->uid == p->suid || current->euid == p->suid)
- return 0;
-
/* sigcont is permitted within same session */
if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p)))
return 0;
--
1.5.1.1.GIT
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