Smack: Signal delivery as an append operation

Under a strict subject/object security policy delivering a
signal or delivering network IPC could be considered either
a write or an append operation. The original choice to make
both write operations leads to an issue where IPC delivery
is desired under policy, but delivery of signals is not.
This patch provides the option of making signal delivery
an append operation, allowing Smack rules that deny signal
delivery while allowing IPC. This was requested for Tizen.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
[mainline backport of commit c60b906673eebb4f65840fa9dc204401caf276ea]
Change-Id: If4d2821381ebb608cefe66e4ca5c3c8469f846f8

diff --git a/security/smack/Kconfig b/security/smack/Kconfig
index 271adae81796c2825797b3941f3bf9fd3481a86b..923b120e0fa5cee6925ac8e2ac4b8b60b8561cec 100644 (file)
--- a/security/smack/Kconfig
+++ b/security/smack/Kconfig
@@ -40,3 +40,15 @@ config SECURITY_SMACK_NETFILTER
          This enables security marking of network packets using
          Smack labels.
          If you are unsure how to answer this question, answer N.
+
+config SECURITY_SMACK_APPEND_SIGNALS
+       bool "Treat delivering signals as an append operation"
+       depends on SECURITY_SMACK
+       default n
+       help
+         Sending a signal has been treated as a write operation to the
+         receiving process. If this option is selected, the delivery
+         will be an append operation instead. This makes it possible
+         to differentiate between delivering a network packet and
+         delivering a signal in the Smack rules.
+         If you are unsure how to answer this question, answer N.

diff --git a/security/smack/smack.h b/security/smack/smack.h
index 6c91156ae2256798e59fb54518efa6d056094d7d..91981f925ed6c95570e87a2231e3aa31d1e7627f 100644 (file)
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -250,6 +250,16 @@ enum {
 #define MAY_LOCK       0x00002000      /* Locks should be writes, but ... */
 #define MAY_BRINGUP    0x00004000      /* Report use of this rule */
 
+/*
+ * The policy for delivering signals is configurable.
+ * It is usually "write", but can be "append".
+ */
+#ifdef CONFIG_SECURITY_SMACK_APPEND_SIGNALS
+#define MAY_DELIVER    MAY_APPEND      /* Signal delivery requires append */
+#else
+#define MAY_DELIVER    MAY_WRITE       /* Signal delivery requires write */
+#endif
+
 #define SMACK_BRINGUP_ALLOW            1       /* Allow bringup mode */
 #define SMACK_UNCONFINED_SUBJECT       2       /* Allow unconfined label */
 #define SMACK_UNCONFINED_OBJECT                3       /* Allow unconfined label */

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 1f481d4b13baf11dcbd29a20240083fe6df3af6c..cde12b21dd0428421d415287d4d79bcb24afc100 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1835,14 +1835,14 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
 
        /* we don't log here as rc can be overriden */
        skp = file->f_security;
-       rc = smk_access(skp, tkp, MAY_WRITE, NULL);
-       rc = smk_bu_note("sigiotask", skp, tkp, MAY_WRITE, rc);
+       rc = smk_access(skp, tkp, MAY_DELIVER, NULL);
+       rc = smk_bu_note("sigiotask", skp, tkp, MAY_DELIVER, rc);
        if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
                rc = 0;
 
        smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
        smk_ad_setfield_u_tsk(&ad, tsk);
-       smack_log(skp->smk_known, tkp->smk_known, MAY_WRITE, rc, &ad);
+       smack_log(skp->smk_known, tkp->smk_known, MAY_DELIVER, rc, &ad);
        return rc;
 }
 
@@ -2240,8 +2240,8 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
         * can write the receiver.
         */
        if (secid == 0) {
-               rc = smk_curacc(tkp, MAY_WRITE, &ad);
-               rc = smk_bu_task(p, MAY_WRITE, rc);
+               rc = smk_curacc(tkp, MAY_DELIVER, &ad);
+               rc = smk_bu_task(p, MAY_DELIVER, rc);
                return rc;
        }
        /*
@@ -2250,8 +2250,8 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
         * we can't take privilege into account.
         */
        skp = smack_from_secid(secid);
-       rc = smk_access(skp, tkp, MAY_WRITE, &ad);
-       rc = smk_bu_note("USB signal", skp, tkp, MAY_WRITE, rc);
+       rc = smk_access(skp, tkp, MAY_DELIVER, &ad);
+       rc = smk_bu_note("USB signal", skp, tkp, MAY_DELIVER, rc);
        return rc;
 }