libselinux: handle null SID's in sidput / sidget

This patch makes it possible to sidput a userspace AVC SID in cleanup code when the SID may never have been initialized.

---

avc_internal.h | 4 ++--

1 file changed, 2 insertions(+), 2 deletions(-)

Index: libselinux/src/avc_internal.h
===================================================================
@@ -18,12 +18,12 @@

/* SID reference counter manipulation */ static inline int sid_inc_refcnt(security_id_t sid) {
- return sid->refcnt = (sid->refcnt > 0) ? sid->refcnt + 1 : 0;
+ return sid->refcnt = (sid && sid->refcnt > 0) ? sid->refcnt + 1 : 0;
}

static inline int sid_dec_refcnt(security_id_t sid) {
- return sid->refcnt = (sid->refcnt > 0) ? sid->refcnt - 1 : 0;
+ return sid->refcnt = (sid && sid->refcnt > 0) ? sid->refcnt - 1 : 0;
}

/* callback pointers */

Eamon Walsh <[email protected]>
National Security Agency


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This patch makes it possible to sidput a userspace AVC SID in cleanup code when the SID may never have been initialized.

This version drops the check in sidget and avoids taking the AVC lock on a null SID (and fixes a null-pointer dereference).

---

avc.c | 2 ++

1 file changed, 2 insertions(+)

Index: libselinux/src/avc.c
===================================================================
@@ -272,6 +272,8 @@

int sidput(security_id_t sid)

{
	int rc;
+	if (!sid)
+	    return 0;
	avc_get_lock(avc_lock);
	rc = sid_dec_refcnt(sid);
	avc_release_lock(avc_lock);

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