From a3c751a50fe6bbe50eb7622a14b18b361804ee0c Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Thu, 14 May 2020 16:44:23 +0200 Subject: vfs: allow unprivileged whiteout creation Whiteouts, unlike real device node should not require privileges to create. The general concern with device nodes is that opening them can have side effects. The kernel already avoids zero major (see Documentation/admin-guide/devices.txt). To be on the safe side the patch explicitly forbids registering a char device with 0/0 number (see cdev_add()). This guarantees that a non-O_PATH open on a whiteout will fail with ENODEV; i.e. it won't have any side effect. Signed-off-by: Miklos Szeredi --- fs/char_dev.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/char_dev.c') diff --git a/fs/char_dev.c b/fs/char_dev.c index c5e6eff5a381..ba0ded7842a7 100644 --- a/fs/char_dev.c +++ b/fs/char_dev.c @@ -483,6 +483,9 @@ int cdev_add(struct cdev *p, dev_t dev, unsigned count) p->dev = dev; p->count = count; + if (WARN_ON(dev == WHITEOUT_DEV)) + return -EBUSY; + error = kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p); if (error) -- cgit v1.2.3-59-g8ed1b