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-rw-r--r--security/selinux/avc.c23
-rw-r--r--security/selinux/hooks.c4
-rw-r--r--security/selinux/include/avc.h1
3 files changed, 25 insertions, 3 deletions
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 635e5c1e3e48..5de18a6d5c3f 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -838,6 +838,7 @@ out:
* @ssid,@tsid,@tclass : identifier of an AVC entry
* @seqno : sequence number when decision was made
* @xpd: extended_perms_decision to be added to the node
+ * @flags: the AVC_* flags, e.g. AVC_NONBLOCKING, AVC_EXTENDED_PERMS, or 0.
*
* if a valid AVC entry doesn't exist,this function returns -ENOENT.
* if kmalloc() called internal returns NULL, this function returns -ENOMEM.
@@ -856,6 +857,23 @@ static int avc_update_node(struct selinux_avc *avc,
struct hlist_head *head;
spinlock_t *lock;
+ /*
+ * If we are in a non-blocking code path, e.g. VFS RCU walk,
+ * then we must not add permissions to a cache entry
+ * because we cannot safely audit the denial. Otherwise,
+ * during the subsequent blocking retry (e.g. VFS ref walk), we
+ * will find the permissions already granted in the cache entry
+ * and won't audit anything at all, leading to silent denials in
+ * permissive mode that only appear when in enforcing mode.
+ *
+ * See the corresponding handling in slow_avc_audit(), and the
+ * logic in selinux_inode_follow_link and selinux_inode_permission
+ * for the VFS MAY_NOT_BLOCK flag, which is transliterated into
+ * AVC_NONBLOCKING for avc_has_perm_noaudit().
+ */
+ if (flags & AVC_NONBLOCKING)
+ return 0;
+
node = avc_alloc_node(avc);
if (!node) {
rc = -ENOMEM;
@@ -1115,7 +1133,7 @@ decision:
* @tsid: target security identifier
* @tclass: target security class
* @requested: requested permissions, interpreted based on @tclass
- * @flags: AVC_STRICT or 0
+ * @flags: AVC_STRICT, AVC_NONBLOCKING, or 0
* @avd: access vector decisions
*
* Check the AVC to determine whether the @requested permissions are granted
@@ -1199,7 +1217,8 @@ int avc_has_perm_flags(struct selinux_state *state,
struct av_decision avd;
int rc, rc2;
- rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, 0,
+ rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested,
+ (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
&avd);
rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index f0e36c3492ba..7f6068489a02 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2982,7 +2982,9 @@ static int selinux_inode_permission(struct inode *inode, int mask)
return PTR_ERR(isec);
rc = avc_has_perm_noaudit(&selinux_state,
- sid, isec->sid, isec->sclass, perms, 0, &avd);
+ sid, isec->sid, isec->sclass, perms,
+ (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
+ &avd);
audited = avc_audit_required(perms, &avd, rc,
from_access ? FILE__AUDIT_ACCESS : 0,
&denied);
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index ef899bcfd2cb..74ea50977c20 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -142,6 +142,7 @@ static inline int avc_audit(struct selinux_state *state,
#define AVC_STRICT 1 /* Ignore permissive mode. */
#define AVC_EXTENDED_PERMS 2 /* update extended permissions */
+#define AVC_NONBLOCKING 4 /* non blocking */
int avc_has_perm_noaudit(struct selinux_state *state,
u32 ssid, u32 tsid,
u16 tclass, u32 requested,