[PATCH RFC 39/41] usb: gadget: f_mass_storage: refuse files on pseudo filesystems

[Christian Brauner <brauner@xxxxxxxxxx>]

fsg_lun_open() takes any regular file as the backing file of a LUN. The
file-storage kthread then reads and writes it with kernel_read() and
kernel_write() on behalf of the USB host. With a procfs or sysfs file
behind a LUN the host gets to read and write kernel interfaces with
kernel credentials. Refuse files on pseudo filesystems just like loop
does.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 drivers/usb/gadget/function/storage_common.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/gadget/function/storage_common.c 
b/drivers/usb/gadget/function/storage_common.c
index 75831f2c7abe..83683ade20c2 100644
--- a/drivers/usb/gadget/function/storage_common.c
+++ b/drivers/usb/gadget/function/storage_common.c
@@ -211,6 +211,11 @@ int fsg_lun_open(struct fsg_lun *curlun, const char 
*filename)
                goto out;
        }
 
+       if (file_is_pseudo(filp)) {
+               LINFO(curlun, "file on a pseudo filesystem: %s\n", filename);
+               goto out;
+       }
+
        /*
         * If we can't read the file, it's no good.
         * If we can't write the file, use it read-only.

-- 
2.53.0