UPSTREAM: ecryptfs: don't allow mmap when the lower fs doesn't support it

(cherry picked from commit f0fe970df3838c202ef6c07a4c2b36838ef0a88b)

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@suse.com>
Cc: stable@vger.kernel.org
[tyhicks: clean up f_op check by using ecryptfs_file_to_lower()]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Change-Id: I66e3670771630a25b0608f10019d1584e9ce73a6
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>

diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index feef8a9c4de7cf09bcbc0effb45f83c207c9015b..11309683d65fb4be48f7a1d3b06f32500869a9e4 100644 (file)
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -170,6 +170,19 @@ 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
@@ -364,7 +377,7 @@ const struct file_operations ecryptfs_main_fops = {
 #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,