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Subject[PATCH 1/3] signals: cleanup security_task_kill() usage/implementation
Every implementation of ->task_kill() does nothing when the signal comes from
the kernel. This is correct, but means that check_kill_permission() should call
security_task_kill() only for SI_FROMUSER() case, and we can remove the same
check from ->task_kill() implementations.

(sadly, check_kill_permission() is the last user of signal->session/__session
but we can't s/task_session_nr/task_session/ here).

NOTE: Eric W. Biederman pointed out cap_task_kill() should die, and I think he
is very right.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

kernel/signal.c | 27 ++++++++++++++-------------
security/commoncap.c | 3 ---
security/selinux/hooks.c | 3 ---
security/smack/smack_lsm.c | 9 ---------
4 files changed, 14 insertions(+), 28 deletions(-)
--- 25/kernel/signal.c~1_LSM_KILL 2008-02-25 18:12:57.000000000 +0300
+++ 25/kernel/signal.c 2008-02-25 18:15:38.000000000 +0300
@@ -526,22 +526,23 @@ static int rm_from_queue(unsigned long m
static int check_kill_permission(int sig, struct siginfo *info,
struct task_struct *t)
{
- int error = -EINVAL;
+ int error;
+
if (!valid_signal(sig))
- return error;
+ return -EINVAL;

- if (info == SEND_SIG_NOINFO || (!is_si_special(info) && SI_FROMUSER(info))) {
- error = audit_signal_info(sig, t); /* Let audit system see the signal */
- if (error)
- return error;
- error = -EPERM;
- if (((sig != SIGCONT) ||
- (task_session_nr(current) != task_session_nr(t)))
- && (current->euid ^ t->suid) && (current->euid ^ t->uid)
- && (current->uid ^ t->suid) && (current->uid ^ t->uid)
- && !capable(CAP_KILL))
+ if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
+ return 0;
+
+ error = audit_signal_info(sig, t); /* Let audit system see the signal */
+ if (error)
return error;
- }
+
+ if (((sig != SIGCONT) || (task_session_nr(current) != task_session_nr(t)))
+ && (current->euid ^ t->suid) && (current->euid ^ t->uid)
+ && (current->uid ^ t->suid) && (current->uid ^ t->uid)
+ && !capable(CAP_KILL))
+ return -EPERM;

return security_task_kill(t, info, sig, 0);
}
--- 25/security/commoncap.c~1_LSM_KILL 2008-02-25 18:07:54.000000000 +0300
+++ 25/security/commoncap.c 2008-02-25 18:52:16.000000000 +0300
@@ -543,9 +543,6 @@ int cap_task_setnice (struct task_struct
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
--- 25/security/smack/smack_lsm.c~1_LSM_KILL 2008-02-15 16:59:20.000000000 +0300
+++ 25/security/smack/smack_lsm.c 2008-02-25 18:54:01.000000000 +0300
@@ -1094,15 +1094,6 @@ static int smack_task_kill(struct task_s
int sig, u32 secid)
{
/*
- * Special cases where signals really ought to go through
- * in spite of policy. Stephen Smalley suggests it may
- * make sense to change the caller so that it doesn't
- * bother with the LSM hook in these cases.
- */
- if (info != SEND_SIG_NOINFO &&
- (is_si_special(info) || SI_FROMKERNEL(info)))
- return 0;
- /*
* Sending a signal requires that the sender
* can write the receiver.
*/
--- 25/security/selinux/hooks.c~1_LSM_KILL 2008-02-15 16:59:20.000000000 +0300
+++ 25/security/selinux/hooks.c 2008-02-25 18:57:23.000000000 +0300
@@ -3194,9 +3194,6 @@ static int selinux_task_kill(struct task
if (rc)
return rc;

- if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
- return 0;
-
if (!sig)
perm = PROCESS__SIGNULL; /* null signal; existence test */
else


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