Commit 70e7af24 authored by Omar Sandoval's avatar Omar Sandoval Committed by Chris Mason

Btrfs: fix delalloc accounting leak caused by u32 overflow

btrfs_calc_trans_metadata_size() does an unsigned 32-bit multiplication,
which can overflow if num_items >= 4 GB / (nodesize * BTRFS_MAX_LEVEL * 2).
For a nodesize of 16kB, this overflow happens at 16k items. Usually,
num_items is a small constant passed to btrfs_start_transaction(), but
we also use btrfs_calc_trans_metadata_size() for metadata reservations
for extent items in btrfs_delalloc_{reserve,release}_metadata().

In drop_outstanding_extents(), num_items is calculated as
inode->reserved_extents - inode->outstanding_extents. The difference
between these two counters is usually small, but if many delalloc
extents are reserved and then the outstanding extents are merged in
btrfs_merge_extent_hook(), the difference can become large enough to
overflow in btrfs_calc_trans_metadata_size().

The overflow manifests itself as a leak of a multiple of 4 GB in
delalloc_block_rsv and the metadata bytes_may_use counter. This in turn
can cause early ENOSPC errors. Additionally, these WARN_ONs in
extent-tree.c will be hit when unmounting:

    WARN_ON(fs_info->delalloc_block_rsv.size > 0);
    WARN_ON(fs_info->delalloc_block_rsv.reserved > 0);
    WARN_ON(space_info->bytes_pinned > 0 ||
            space_info->bytes_reserved > 0 ||
            space_info->bytes_may_use > 0);

Fix it by casting nodesize to a u64 so that
btrfs_calc_trans_metadata_size() does a full 64-bit multiplication.
While we're here, do the same in btrfs_calc_trunc_metadata_size(); this
can't overflow with any existing uses, but it's better to be safe here
than have another hard-to-debug problem later on.

Signed-off-by: default avatarOmar Sandoval <>
Reviewed-by: default avatarDavid Sterba <>
Signed-off-by: default avatarChris Mason <>
parent 452e62b7
......@@ -2564,7 +2564,7 @@ u64 btrfs_csum_bytes_to_leaves(struct btrfs_fs_info *fs_info, u64 csum_bytes);
static inline u64 btrfs_calc_trans_metadata_size(struct btrfs_fs_info *fs_info,
unsigned num_items)
return fs_info->nodesize * BTRFS_MAX_LEVEL * 2 * num_items;
return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * 2 * num_items;
......@@ -2574,7 +2574,7 @@ static inline u64 btrfs_calc_trans_metadata_size(struct btrfs_fs_info *fs_info,
static inline u64 btrfs_calc_trunc_metadata_size(struct btrfs_fs_info *fs_info,
unsigned num_items)
return fs_info->nodesize * BTRFS_MAX_LEVEL * num_items;
return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * num_items;
int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans,
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