[PATCH 4.14 20/50] dump_common_audit_data(): fix racy accesses to ->d_name

[Greg Kroah-Hartman]

From: Al Viro <v...@zeniv.linux.org.uk>

commit d36a1dd9f77ae1e72da48f4123ed35627848507d 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: sta...@kernel.org # v2.6.2+
Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 security/lsm_audit.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/security/lsm_audit.c
+++ b/security/lsm_audit.c
@@ -277,7 +277,9 @@ static void dump_common_audit_data(struc
                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(struc
                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=");