dump_common_audit_data(): fix racy accesses to ->d_name

stable inclusion
from linux-4.19.169
commit fda4bb55c45bd9fdf490c39c3e567f0cea931e54

--------------------------------

commit d36a1dd9 upstream.

We are not guaranteed the locking environment that would prevent
dentry getting renamed right under us.  And it's possible for
old long name to be freed after rename, leading to UAF here.

Cc: stable@kernel.org # v2.6.2+
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

security/lsm_audit.c

@@ -277,7 +277,9 @@ static void dump_common_audit_data(struct audit_buffer *ab,
 		struct inode *inode;
 
 		audit_log_format(ab, " name=");
+		spin_lock(&a->u.dentry->d_lock);
 		audit_log_untrustedstring(ab, a->u.dentry->d_name.name);
+		spin_unlock(&a->u.dentry->d_lock);
 
 		inode = d_backing_inode(a->u.dentry);
 		if (inode) {
@@ -295,8 +297,9 @@ static void dump_common_audit_data(struct audit_buffer *ab,
 		dentry = d_find_alias(inode);
 		if (dentry) {
 			audit_log_format(ab, " name=");
-			audit_log_untrustedstring(ab,
-					 dentry->d_name.name);
+			spin_lock(&dentry->d_lock);
+			audit_log_untrustedstring(ab, dentry->d_name.name);
+			spin_unlock(&dentry->d_lock);
 			dput(dentry);
 		}
 		audit_log_format(ab, " dev=");