linux-kernel - [PATCH] fs/fuse: Fix matching of FUSE_DEV_IOC

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Message-Id: <20210319150514.1315985-1-balsini@android.com>
Date:   Fri, 19 Mar 2021 15:05:14 +0000
From:   Alessio Balsini <balsini@...roid.com>
To:     Arnd Bergmann <arnd@...nel.org>, Miklos Szeredi <miklos@...redi.hu>
Cc:     kernel-team@...roid.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fs/fuse: Fix matching of FUSE_DEV_IOC_CLONE command

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>
---
 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);
-- 
2.31.0.291.g576ba9dcdaf-goog