fs: require inode_owner_or_capable for F_SET_RW_HINT

F_SET_RW_HINT controls data placement in the file system and / or
device and should not be available to everyone who can read a given file.

Signed-off-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: Christoph Hellwig

fs/fcntl.c

@@ -374,6 +374,9 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 	u64 __user *argp = (u64 __user *)arg;
 	u64 hint;
 
+	if (!inode_owner_or_capable(file_mnt_idmap(file), inode))
+		return -EPERM;
+
 	if (copy_from_user(&hint, argp, sizeof(hint)))
 		return -EFAULT;
 	if (!rw_hint_valid(hint))