From: Richard Weinberger <richard@nod.at>
Date: Fri, 16 Sep 2016 09:45:24 +0000 (+0200)
Subject: ovl: Fix info leak in ovl_lookup_temp()
X-Git-Tag: firefly_0821_release~176^2~4^2~22^2~67
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=0a5600d83fa5a251c91459779d5311a005e4c5b3;p=firefly-linux-kernel-4.4.55.git

ovl: Fix info leak in ovl_lookup_temp()

commit 6a45b3628ce4dcf7498b39c87d475bab6e2a9b24 upstream.

The function uses the memory address of a struct dentry as unique id.
While the address-based directory entry is only visible to root it is IMHO
still worth fixing since the temporary name does not have to be a kernel
address.  It can be any unique number.  Replace it by an atomic integer
which is allowed to wrap around.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: e9be9d5e76e3 ("overlay filesystem")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index ba5ef733951f..327177df03a5 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -12,6 +12,7 @@
 #include <linux/xattr.h>
 #include <linux/security.h>
 #include <linux/cred.h>
+#include <linux/atomic.h>
 #include "overlayfs.h"
 
 void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
@@ -35,8 +36,10 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry)
 {
 	struct dentry *temp;
 	char name[20];
+	static atomic_t temp_id = ATOMIC_INIT(0);
 
-	snprintf(name, sizeof(name), "#%lx", (unsigned long) dentry);
+	/* counter is allowed to wrap, since temp dentries are ephemeral */
+	snprintf(name, sizeof(name), "#%x", atomic_inc_return(&temp_id));
 
 	temp = lookup_one_len(name, workdir, strlen(name));
 	if (!IS_ERR(temp) && temp->d_inode) {