ecryptfs: forbid opening files without mmap handler

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@google.com>
Acked-by: Tyler Hicks <tyhicks@canonical.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/ecryptfs/kthread.c b/fs/ecryptfs/kthread.c
index 866bb18efefea9953250ba1cbdc145e7d4be49af..e818f5ac7a2692b6bb5c1a132d7bbfd967ad956a 100644 (file)
--- 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 **lower_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 **lower_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;
 }