[PATCH 4.4 45/75] ecryptfs: forbid opening files without mmap handler

From: Greg Kroah-Hartman
Date: Wed Jun 22 2016 - 18:45:36 EST


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

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

From: Jann Horn <jannh@xxxxxxxxxx>

commit 2f36db71009304b3f0b95afacd8eba1f9f046b87 upstream.

This prevents users from triggering a stack overflow through a recursive
invocation of pagefault handling that involves mapping procfs files into
virtual memory.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/ecryptfs/kthread.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

--- a/fs/ecryptfs/kthread.c
+++ b/fs/ecryptfs/kthread.c
@@ -25,6 +25,7 @@
#include <linux/slab.h>
#include <linux/wait.h>
#include <linux/mount.h>
+#include <linux/file.h>
#include "ecryptfs_kernel.h"

struct ecryptfs_open_req {
@@ -147,7 +148,7 @@ int ecryptfs_privileged_open(struct file
flags |= IS_RDONLY(d_inode(lower_dentry)) ? O_RDONLY : O_RDWR;
(*lower_file) = dentry_open(&req.path, flags, cred);
if (!IS_ERR(*lower_file))
- goto out;
+ goto have_file;
if ((flags & O_ACCMODE) == O_RDONLY) {
rc = PTR_ERR((*lower_file));
goto out;
@@ -165,8 +166,16 @@ int ecryptfs_privileged_open(struct file
mutex_unlock(&ecryptfs_kthread_ctl.mux);
wake_up(&ecryptfs_kthread_ctl.wait);
wait_for_completion(&req.done);
- if (IS_ERR(*lower_file))
+ if (IS_ERR(*lower_file)) {
rc = PTR_ERR(*lower_file);
+ goto out;
+ }
+have_file:
+ if ((*lower_file)->f_op->mmap == NULL) {
+ fput(*lower_file);
+ *lower_file = NULL;
+ rc = -EMEDIUMTYPE;
+ }
out:
return rc;
}