linux-kernel - [PATCH 5.12 570/677] fuse: fix matching of FUSE_DEV_IOC

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Message-Id: <20210512144856.333623127@linuxfoundation.org>
Date:   Wed, 12 May 2021 16:50:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        Alessio Balsini <balsini@...roid.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.12 570/677] fuse: fix matching of FUSE_DEV_IOC_CLONE command

From: Alessio Balsini <balsini@...roid.com>

[ Upstream commit 6076f5f341e612152879bfda99f0b76c1953bf0b ]

With commit f8425c939663 ("fuse: 32-bit user space ioctl compat for fuse
device") the matching constraints for the FUSE_DEV_IOC_CLONE ioctl command
are relaxed, limited to the testing of command type and number.  As Arnd
noticed, this is wrong as it wouldn't ensure the correctness of the data
size or direction for the received FUSE device ioctl.

Fix by bringing back the comparison of the ioctl received by the FUSE
device to the originally generated FUSE_DEV_IOC_CLONE.

Fixes: f8425c939663 ("fuse: 32-bit user space ioctl compat for fuse device")
Reported-by: Arnd Bergmann <arnd@...nel.org>
Signed-off-by: Alessio Balsini <balsini@...roid.com>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/fuse/dev.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index c0fee830a34e..a5ceccc5ef00 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2233,11 +2233,8 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 	int oldfd;
 	struct fuse_dev *fud = NULL;
 
-	if (_IOC_TYPE(cmd) != FUSE_DEV_IOC_MAGIC)
-		return -ENOTTY;
-
-	switch (_IOC_NR(cmd)) {
-	case _IOC_NR(FUSE_DEV_IOC_CLONE):
+	switch (cmd) {
+	case FUSE_DEV_IOC_CLONE:
 		res = -EFAULT;
 		if (!get_user(oldfd, (__u32 __user *)arg)) {
 			struct file *old = fget(oldfd);
-- 
2.30.2