Btrfs: buffer results in the space_info ioctl

The space_info ioctl was using copy_to_user inside rcu_read_lock.  This
commit changes things to copy into a buffer first and then dump the
result down to userland.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 38a6886..4329610 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1848,39 +1848,74 @@ long btrfs_ioctl_space_info(struct btrfs_root *root, void __user *arg)
        struct btrfs_ioctl_space_args space_args;
        struct btrfs_ioctl_space_info space;
        struct btrfs_ioctl_space_info *dest;
+       struct btrfs_ioctl_space_info *dest_orig;
+       struct btrfs_ioctl_space_info *user_dest;
        struct btrfs_space_info *info;
+       int alloc_size;
        int ret = 0;
+       int slot_count = 0;
 
        if (copy_from_user(&space_args,
                           (struct btrfs_ioctl_space_args __user *)arg,
                           sizeof(space_args)))
                return -EFAULT;
 
+       /* first we count slots */
+       rcu_read_lock();
+       list_for_each_entry_rcu(info, &root->fs_info->space_info, list)
+               slot_count++;
+       rcu_read_unlock();
+
+       /* space_slots == 0 means they are asking for a count */
+       if (space_args.space_slots == 0) {
+               space_args.total_spaces = slot_count;
+               goto out;
+       }
+       alloc_size = sizeof(*dest) * slot_count;
+       /* we generally have at most 6 or so space infos, one for each raid
+        * level.  So, a whole page should be more than enough for everyone
+        */
+       if (alloc_size > PAGE_CACHE_SIZE)
+               return -ENOMEM;
+
        space_args.total_spaces = 0;
-       dest = (struct btrfs_ioctl_space_info *)
-               (arg + sizeof(struct btrfs_ioctl_space_args));
+       dest = kmalloc(alloc_size, GFP_NOFS);
+       if (!dest)
+               return -ENOMEM;
+       dest_orig = dest;
 
+       /* now we have a buffer to copy into */
        rcu_read_lock();
        list_for_each_entry_rcu(info, &root->fs_info->space_info, list) {
-               if (!space_args.space_slots) {
-                       space_args.total_spaces++;
-                       continue;
-               }
+               /* make sure we don't copy more than we allocated
+                * in our buffer
+                */
+               if (slot_count == 0)
+                       break;
+               slot_count--;
+
+               /* make sure userland has enough room in their buffer */
                if (space_args.total_spaces >= space_args.space_slots)
                        break;
+
                space.flags = info->flags;
                space.total_bytes = info->total_bytes;
                space.used_bytes = info->bytes_used;
-               if (copy_to_user(dest, &space, sizeof(space))) {
-                       ret = -EFAULT;
-                       break;
-               }
+               memcpy(dest, &space, sizeof(space));
                dest++;
                space_args.total_spaces++;
        }
        rcu_read_unlock();
 
-       if (copy_to_user(arg, &space_args, sizeof(space_args)))
+       user_dest = (struct btrfs_ioctl_space_info *)
+               (arg + sizeof(struct btrfs_ioctl_space_args));
+
+       if (copy_to_user(user_dest, dest_orig, alloc_size))
+               ret = -EFAULT;
+
+       kfree(dest_orig);
+out:
+       if (ret == 0 && copy_to_user(arg, &space_args, sizeof(space_args)))
                ret = -EFAULT;
 
        return ret;