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SubjectRe: [PATCH 1/1] file capabilities: remove cap_task_kill() (-git)
Quoting Linus Torvalds (torvalds@linux-foundation.org):
>
>
> On Wed, 19 Mar 2008, Serge E. Hallyn wrote:
> >
> > 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.
>
> Ok, now I'm _really_ confused. I have smack in my tree, it got merged
> before -rc1.

No clearly I'm the one confused/on drugs.

I see it now. I swear I checked my own freshly pulled tree and
gitweb several times...

> So any patch that is against some version without smack is not a patch
> against a -git tree for the last several weeks.
>
> Me confused.
>
> Linus

New patch against -git attached.

thanks,
-serge


From a0e56351e00b7b7442723b7ca6247c267c2628fd Mon Sep 17 00:00:00 2001
From: Serge Hallyn <serge@hallyn.com>
Date: Fri, 29 Feb 2008 15:14:57 +0000
Subject: [PATCH 1/1] file capabilities: remove cap_task_kill() (-git)
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@hallyn.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
---
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 b07357c..c673dfd 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -57,7 +57,6 @@ 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);
@@ -2187,7 +2186,7 @@ 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 38d7075..732ba27 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;
/*
* 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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