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>

1 files changed, 46 insertions, 11 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 38a68863390a..4329610b141b 100644
--- 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;