Commit 292cbd51 authored Nov 26, 2014 by Filipe Manana Committed by Chris Mason Dec 02, 2014

Btrfs: fix invalid block group rbtree access after bg is removed



If we grab a block group, for example in btrfs_trim_fs(), we will be holding
a reference on it but the block group can be removed after we got it (via
btrfs_remove_block_group), which means it will no longer be part of the
rbtree.

However, btrfs_remove_block_group() was only calling rb_erase() which leaves
the block group's rb_node left and right child pointers with the same content
they had before calling rb_erase. This was dangerous because a call to
next_block_group() would access the node's left and right child pointers (via
rb_next), which can be no longer valid.

Fix this by clearing a block group's node after removing it from the tree,
and have next_block_group() do a tree search to get the next block group
instead of using rb_next() if our block group was removed.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

parent 9ea24bbe

fs/btrfs/extent-tree.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -3162,7 +3162,19 @@ next_block_group(struct btrfs_root *root,
		struct btrfs_block_group_cache *cache)
		{
		struct rb_node *node;

		spin_lock(&root->fs_info->block_group_cache_lock);

		/* If our block group was removed, we need a full search. */
		if (RB_EMPTY_NODE(&cache->cache_node)) {
		const u64 next_bytenr = cache->key.objectid + cache->key.offset;

		spin_unlock(&root->fs_info->block_group_cache_lock);
		btrfs_put_block_group(cache);
		cache = btrfs_lookup_first_block_group(root->fs_info,
		next_bytenr);
		return cache;
		}
		node = rb_next(&cache->cache_node);
		btrfs_put_block_group(cache);
		if (node) {
		@@ -9389,6 +9401,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
		spin_lock(&root->fs_info->block_group_cache_lock);
		rb_erase(&block_group->cache_node,
		&root->fs_info->block_group_cache_tree);
		RB_CLEAR_NODE(&block_group->cache_node);

		if (root->fs_info->first_logical_byte == block_group->key.objectid)
		root->fs_info->first_logical_byte = (u64)-1;

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