linux-kernel - [PATCH 3.10 097/180] ecryptfs: forbid opening files without mmap handler

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Date:   Sun, 21 Aug 2016 17:30:27 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 097/180] ecryptfs: forbid opening files without mmap handler

From: Jann Horn <jannh@...gle.com>

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@...gle.com>
Acked-by: Tyler Hicks <tyhicks@...onical.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 fs/ecryptfs/kthread.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/ecryptfs/kthread.c b/fs/ecryptfs/kthread.c
index f1ea610..9b661a4 100644
--- 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(lower_dentry->d_inode) ? 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;
 }
-- 
2.8.0.rc2.1.gbe9624a