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From ec4eb03af07b0fbc330aecca6ac4ebd6accd8825 Mon Sep 17 00:00:00 2001
From: Rafal Krypa <r.krypa@samsung.com>
Date: Mon, 4 Apr 2016 11:14:53 +0200
Subject: [PATCH 3/4] Smack: ignore null signal in smack_task_kill
Kill with signal number 0 is commonly used for checking PID existence.
Smack treated such cases like any other kills, although no signal is
actually delivered when sig == 0.
Checking permissions when sig == 0 didn't prevent an unprivileged caller
from learning whether PID exists or not. When it existed, kernel returned
EPERM, when it didn't - ESRCH. The only effect of policy check in such
case is noise in audit logs.
This change lets Smack silently ignore kill() invocations with sig == 0.
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
---
security/smack/smack_lsm.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index b2bcb14..cf8a93f 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2239,6 +2239,9 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
struct smack_known *tkp = smk_of_task_struct(p);
int rc;
+ if (!sig)
+ return 0; /* null signal; existence test */
+
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
smk_ad_setfield_u_tsk(&ad, p);
/*
--
2.7.4
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