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

[ Upstream 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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index 72afcc629d7b1fee2963fb90e1691a221eb77d8e..f56a4216d081e711686080b6a81d5d8689029bee 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
@@ -365,7 +378,7 @@ 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,