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

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[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 929be17a9b49 ("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: 929be17a9b49 ("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>
This commit is contained in:
Qu Wenruo 2020-07-31 19:29:11 +08:00 committed by David Sterba
parent 881a3a11c2
commit c57dd1f2f6
3 changed files with 20 additions and 0 deletions
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2
fs/btrfs/extent-io-tree.h
View File

@ -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,

14
fs/btrfs/extent-tree.c
View File

@ -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);

4
fs/btrfs/volumes.c
View File

@ -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,