linux-kernel - [PATCH 4.2.y-ckt 024/268] ovl: setattr: check permissions before copy-up

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Date:	Wed, 27 Jan 2016 12:31:25 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 024/268] ovl: setattr: check permissions before copy-up

4.2.8-ckt3 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Miklos Szeredi <miklos@...redi.hu>

commit cf9a6784f7c1b5ee2b9159a1246e327c331c5697 upstream.

Without this copy-up of a file can be forced, even without actually being
allowed to do anything on the file.

[Arnd Bergmann] include <linux/pagemap.h> for PAGE_CACHE_SIZE (used by
MAX_LFS_FILESIZE definition).

Signed-off-by: Miklos Szeredi <miklos@...redi.hu>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 fs/overlayfs/inode.c | 13 +++++++++++++
 fs/overlayfs/super.c |  2 ++
 2 files changed, 15 insertions(+)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 9612849..34300c2 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -45,6 +45,19 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 	int err;
 	struct dentry *upperdentry;
 
+	/*
+	 * Check for permissions before trying to copy-up.  This is redundant
+	 * since it will be rechecked later by ->setattr() on upper dentry.  But
+	 * without this, copy-up can be triggered by just about anybody.
+	 *
+	 * We don't initialize inode->size, which just means that
+	 * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
+	 * check for a swapfile (which this won't be anyway).
+	 */
+	err = inode_change_ok(dentry->d_inode, attr);
+	if (err)
+		return err;
+
 	err = ovl_want_write(dentry);
 	if (err)
 		goto out;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ff82665..f42c940 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -9,6 +9,7 @@
 
 #include <linux/fs.h>
 #include <linux/namei.h>
+#include <linux/pagemap.h>
 #include <linux/xattr.h>
 #include <linux/security.h>
 #include <linux/mount.h>
@@ -910,6 +911,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	sb->s_stack_depth = 0;
+	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	if (ufs->config.upperdir) {
 		if (!ufs->config.workdir) {
 			pr_err("overlayfs: missing 'workdir'\n");
-- 
1.9.1