AUDIT: Avoid sleeping function in SElinux AVC audit.

This patch changes the SELinux AVC to defer logging of paths to the audit
framework upon syscall exit, by saving a reference to the (dentry,vfsmount)
pair in an auxiliary audit item on the current audit context for processing
by audit_log_exit.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/audit.h

@@ -69,6 +69,7 @@
 
 #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
 #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
+#define AUDIT_AVC_PATH		1402	/* dentry, vfsmount pair from avc */
 
 #define AUDIT_KERNEL		2000	/* Asynchronous audit record. NOT A REQUEST. */
 
@@ -225,6 +226,7 @@ extern uid_t audit_get_loginuid(struct audit_context *ctx);
 extern int audit_ipc_perms(unsigned long qbytes, uid_t uid, gid_t gid, mode_t mode);
 extern int audit_socketcall(int nargs, unsigned long *args);
 extern int audit_sockaddr(int len, void *addr);
+extern int audit_avc_path(struct dentry *dentry, struct vfsmount *mnt);
 extern void audit_signal_info(int sig, struct task_struct *t);
 #else
 #define audit_alloc(t) ({ 0; })
@@ -240,6 +242,7 @@ extern void audit_signal_info(int sig, struct task_struct *t);
 #define audit_ipc_perms(q,u,g,m) ({ 0; })
 #define audit_socketcall(n,a) ({ 0; })
 #define audit_sockaddr(len, addr) ({ 0; })
+#define audit_avc_path(dentry, mnt) ({ 0; })
 #define audit_signal_info(s,t) do { ; } while (0)
 #endif
 

kernel/auditsc.c

@@ -34,6 +34,7 @@
 #include <asm/types.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/socket.h>
 #include <linux/audit.h>
 #include <linux/personality.h>
@@ -124,6 +125,11 @@ struct audit_aux_data_sockaddr {
 	char			a[0];
 };
 
+struct audit_aux_data_path {
+	struct audit_aux_data	d;
+	struct dentry		*dentry;
+	struct vfsmount		*mnt;
+};
 
 /* The per-task audit context. */
 struct audit_context {
@@ -553,6 +559,11 @@ static inline void audit_free_aux(struct audit_context *context)
 	struct audit_aux_data *aux;
 
 	while ((aux = context->aux)) {
+		if (aux->type == AUDIT_AVC_PATH) {
+			struct audit_aux_data_path *axi = (void *)aux;
+			dput(axi->dentry);
+			mntput(axi->mnt);
+		}
 		context->aux = aux->next;
 		kfree(aux);
 	}
@@ -724,6 +735,14 @@ static void audit_log_exit(struct audit_context *context)
 			audit_log_format(ab, "saddr=");
 			audit_log_hex(ab, axs->a, axs->len);
 			break; }
+
+		case AUDIT_AVC_PATH: {
+			struct audit_aux_data_path *axi = (void *)aux;
+			audit_log_d_path(ab, "path=", axi->dentry, axi->mnt);
+			dput(axi->dentry);
+			mntput(axi->mnt);
+			break; }
+
 		}
 		audit_log_end(ab);
 
@@ -1124,6 +1143,27 @@ int audit_sockaddr(int len, void *a)
 	return 0;
 }
 
+int audit_avc_path(struct dentry *dentry, struct vfsmount *mnt)
+{
+	struct audit_aux_data_path *ax;
+	struct audit_context *context = current->audit_context;
+
+	if (likely(!context))
+		return 0;
+
+	ax = kmalloc(sizeof(*ax), GFP_ATOMIC);
+	if (!ax)
+		return -ENOMEM;
+
+	ax->dentry = dget(dentry);
+	ax->mnt = mntget(mnt);
+
+	ax->d.type = AUDIT_AVC_PATH;
+	ax->d.next = context->aux;
+	context->aux = (void *)ax;
+	return 0;
+}
+
 void audit_signal_info(int sig, struct task_struct *t)
 {
 	extern pid_t audit_sig_pid;

security/selinux/avc.c

@@ -573,13 +573,10 @@ void avc_audit(u32 ssid, u32 tsid,
 		case AVC_AUDIT_DATA_FS:
 			if (a->u.fs.dentry) {
 				struct dentry *dentry = a->u.fs.dentry;
-				if (a->u.fs.mnt) {
-					audit_log_d_path(ab, "path=", dentry,
-							a->u.fs.mnt);
-				} else {
-					audit_log_format(ab, " name=%s",
-							 dentry->d_name.name);
-				}
+				if (a->u.fs.mnt)
+					audit_avc_path(dentry, a->u.fs.mnt);
+				audit_log_format(ab, " name=%s",
+						 dentry->d_name.name);
 				inode = dentry->d_inode;
 			} else if (a->u.fs.inode) {
 				struct dentry *dentry;
@@ -630,8 +627,10 @@ void avc_audit(u32 ssid, u32 tsid,
 				case AF_UNIX:
 					u = unix_sk(sk);
 					if (u->dentry) {
-						audit_log_d_path(ab, "path=",
-							u->dentry, u->mnt);
+						audit_avc_path(u->dentry, u->mnt);
+						audit_log_format(ab, " name=%s",
+								 u->dentry->d_name.name);
+
 						break;
 					}
 					if (!u->addr)