linux-kernel - [PATCH 3.16 271/305] ecryptfs: don't allow mmap when the lower fs doesn't support it

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Message-ID: <lsq.1471110171.875603820@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jeff Mahoney" <jeffm@...e.com>,
	"Tyler Hicks" <tyhicks@...onical.com>
Subject: [PATCH 3.16 271/305] ecryptfs: don't allow mmap when the lower fs
 doesn't support it

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jeff Mahoney <jeffm@...e.com>

commit f0fe970df3838c202ef6c07a4c2b36838ef0a88b upstream.

There are legitimate reasons to disallow mmap on certain files, notably
in sysfs or procfs.  We shouldn't emulate mmap support on file systems
that don't offer support natively.

CVE-2016-1583

Signed-off-by: Jeff Mahoney <jeffm@...e.com>
[tyhicks: clean up f_op check by using ecryptfs_file_to_lower()]
Signed-off-by: Tyler Hicks <tyhicks@...onical.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ecryptfs/file.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -177,6 +177,19 @@ out:
 	return rc;
 }
 
+static int ecryptfs_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct file *lower_file = ecryptfs_file_to_lower(file);
+	/*
+	 * Don't allow mmap on top of file systems that don't support it
+	 * natively.  If FILESYSTEM_MAX_STACK_DEPTH > 2 or ecryptfs
+	 * allows recursive mounting, this will need to be extended.
+	 */
+	if (!lower_file->f_op->mmap)
+		return -ENODEV;
+	return generic_file_mmap(file, vma);
+}
+
 /**
  * ecryptfs_open
  * @inode: inode speciying file to open
@@ -374,7 +387,7 @@ const struct file_operations ecryptfs_ma
 #ifdef CONFIG_COMPAT
 	.compat_ioctl = ecryptfs_compat_ioctl,
 #endif
-	.mmap = generic_file_mmap,
+	.mmap = ecryptfs_mmap,
 	.open = ecryptfs_open,
 	.flush = ecryptfs_flush,
 	.release = ecryptfs_release,