FAILED: patch "[PATCH] Btrfs: fix delalloc accounting leak caused by u32 overflow" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Omar Sandoval <[email protected]>
Date: Fri, 2 Jun 2017 01:20:01 -0700
Subject: [PATCH] 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.

index 1e82516fe2d8..43a8c42cdf07 100644
@@ -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,