linux-kernel - [PATCH RESEND V12 2/8] fuse: 32-bit user space ioctl compat for fuse device

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Message-Id: <20210125153057.3623715-3-balsini@android.com>
Date:   Mon, 25 Jan 2021 15:30:51 +0000
From:   Alessio Balsini <balsini@...roid.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Akilesh Kailash <akailash@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Antonio SJ Musumeci <trapexit@...wn.link>,
        David Anderson <dvander@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Lawrence <paullawrence@...gle.com>,
        Peng Tao <bergwolf@...il.com>,
        Stefano Duo <duostefano93@...il.com>,
        Zimuzo Ezeozue <zezeozue@...gle.com>, wuyan <wu-yan@....com>,
        fuse-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH RESEND V12 2/8] fuse: 32-bit user space ioctl compat for fuse device

With a 64-bit kernel build the FUSE device cannot handle ioctl requests
coming from 32-bit user space.
This is due to the ioctl command translation that generates different
command identifiers that thus cannot be used for direct comparisons
without proper manipulation.

Explicitly extract type and number from the ioctl command to enable
32-bit user space compatibility on 64-bit kernel builds.

Signed-off-by: Alessio Balsini <balsini@...roid.com>
---
 fs/fuse/dev.c             | 29 ++++++++++++++++++-----------
 include/uapi/linux/fuse.h |  3 ++-
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 588f8d1240aa..ff9f3b83f879 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2233,37 +2233,44 @@ static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
 static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 			   unsigned long arg)
 {
-	int err = -ENOTTY;
+	int res;
+	int oldfd;
+	struct fuse_dev *fud = NULL;
 
-	if (cmd == FUSE_DEV_IOC_CLONE) {
-		int oldfd;
+	if (_IOC_TYPE(cmd) != FUSE_DEV_IOC_MAGIC)
+		return -EINVAL;
 
-		err = -EFAULT;
-		if (!get_user(oldfd, (__u32 __user *) arg)) {
+	switch (_IOC_NR(cmd)) {
+	case _IOC_NR(FUSE_DEV_IOC_CLONE):
+		res = -EFAULT;
+		if (!get_user(oldfd, (__u32 __user *)arg)) {
 			struct file *old = fget(oldfd);
 
-			err = -EINVAL;
+			res = -EINVAL;
 			if (old) {
-				struct fuse_dev *fud = NULL;
-
 				/*
 				 * Check against file->f_op because CUSE
 				 * uses the same ioctl handler.
 				 */
 				if (old->f_op == file->f_op &&
-				    old->f_cred->user_ns == file->f_cred->user_ns)
+				    old->f_cred->user_ns ==
+					    file->f_cred->user_ns)
 					fud = fuse_get_dev(old);
 
 				if (fud) {
 					mutex_lock(&fuse_mutex);
-					err = fuse_device_clone(fud->fc, file);
+					res = fuse_device_clone(fud->fc, file);
 					mutex_unlock(&fuse_mutex);
 				}
 				fput(old);
 			}
 		}
+		break;
+	default:
+		res = -ENOTTY;
+		break;
 	}
-	return err;
+	return res;
 }
 
 const struct file_operations fuse_dev_operations = {
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 98ca64d1beb6..54442612c48b 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -903,7 +903,8 @@ struct fuse_notify_retrieve_in {
 };
 
 /* Device ioctls: */
-#define FUSE_DEV_IOC_CLONE	_IOR(229, 0, uint32_t)
+#define FUSE_DEV_IOC_MAGIC		229
+#define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
 
 struct fuse_lseek_in {
 	uint64_t	fh;
-- 
2.30.0.280.ga3ce27912f-goog