Commit c57dd1f2 authored Jul 31, 2020 by Qu Wenruo Committed by David Sterba Aug 12, 2020

btrfs: trim: fix underflow in trim length to prevent access beyond device boundary

[BUG]
The following script can lead to tons of beyond device boundary access:

  mkfs.btrfs -f $dev -b 10G
  mount $dev $mnt
  trimfs $mnt
  btrfs filesystem resize 1:-1G $mnt
  trimfs $mnt

[CAUSE]
Since commit 929be17a ("btrfs: Switch btrfs_trim_free_extents to
find_first_clear_extent_bit"), we try to avoid trimming ranges that's
already trimmed.

So we check device->alloc_state by finding the first range which doesn't
have CHUNK_TRIMMED and CHUNK_ALLOCATED not set.

But if we shrunk the device, that bits are not cleared, thus we could
easily got a range starts beyond the shrunk device size.

This results the returned @start and @end are all beyond device size,
then we call "end = min(end, device->total_bytes -1);" making @end
smaller than device size.

Then finally we goes "len = end - start + 1", totally underflow the
result, and lead to the beyond-device-boundary access.

[FIX]
This patch will fix the problem in two ways:

- Clear CHUNK_TRIMMED | CHUNK_ALLOCATED bits when shrinking device
  This is the root fix

- Add extra safety check when trimming free device extents
  We check and warn if the returned range is already beyond current
  device.

Link: https://github.com/kdave/btrfs-progs/issues/282


Fixes: 929be17a ("btrfs: Switch btrfs_trim_free_extents to find_first_clear_extent_bit")
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 881a3a11

fs/btrfs/extent-io-tree.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -34,6 +34,8 @@ struct io_failure_record;
		*/
		#define CHUNK_ALLOCATED EXTENT_DIRTY
		#define CHUNK_TRIMMED EXTENT_DEFRAG
		#define CHUNK_STATE_MASK (CHUNK_ALLOCATED \| \
		CHUNK_TRIMMED)

		enum {
		IO_TREE_FS_PINNED_EXTENTS,

fs/btrfs/extent-tree.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -33,6 +33,7 @@
		#include "delalloc-space.h"
		#include "block-group.h"
		#include "discard.h"
		#include "rcu-string.h"

		#undef SCRAMBLE_DELAYED_REFS

		@@ -5668,6 +5669,19 @@ static int btrfs_trim_free_extents(struct btrfs_device device, u64 trimmed)
		&start, &end,
		CHUNK_TRIMMED \| CHUNK_ALLOCATED);

		/* Check if there are any CHUNK_* bits left */
		if (start > device->total_bytes) {
		WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
		btrfs_warn_in_rcu(fs_info,
		"ignoring attempt to trim beyond device size: offset %llu length %llu device %s device size %llu",
		start, end - start + 1,
		rcu_str_deref(device->name),
		device->total_bytes);
		mutex_unlock(&fs_info->chunk_mutex);
		ret = 0;
		break;
		}

		/* Ensure we skip the reserved area in the first 1M */
		start = max_t(u64, start, SZ_1M);

fs/btrfs/volumes.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -4720,6 +4720,10 @@ again:
		}

		mutex_lock(&fs_info->chunk_mutex);
		/* Clear all state bits beyond the shrunk device size */
		clear_extent_bits(&device->alloc_state, new_size, (u64)-1,
		CHUNK_STATE_MASK);

		btrfs_device_set_disk_total_bytes(device, new_size);
		if (list_empty(&device->post_commit_list))
		list_add_tail(&device->post_commit_list,

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