btrfs: check superblock to ensure the fs was not modified at thaw time
[BACKGROUND]
There is an incident report that, one user hibernated the system, with
one btrfs on removable device still mounted.
Then by some incident, the btrfs got mounted and modified by another
system/OS, then back to the hibernated system.
After resuming from the hibernation, new write happened into the victim btrfs.
Now the fs is completely broken, since the underlying btrfs is no longer
the same one before the hibernation, and the user lost their data due to
various transid mismatch.
[REPRODUCER]
We can emulate the situation using the following small script:
truncate -s 1G $dev
mkfs.btrfs -f $dev
mount $dev $mnt
fsstress -w -d $mnt -n 500
sync
xfs_freeze -f $mnt
cp $dev $dev.backup
# There is no way to mount the same cloned fs on the same system,
# as the conflicting fsid will be rejected by btrfs.
# Thus here we have to wipe the fs using a different btrfs.
mkfs.btrfs -f $dev.backup
dd if=$dev.backup of=$dev bs=1M
xfs_freeze -u $mnt
fsstress -w -d $mnt -n 20
umount $mnt
btrfs check $dev
The final fsck will fail due to some tree blocks has incorrect fsid.
This is enough to emulate the problem hit by the unfortunate user.
[ENHANCEMENT]
Although such case should not be that common, it can still happen from
time to time.
From the view of btrfs, we can detect any unexpected super block change,
and if there is any unexpected change, we just mark the fs read-only,
and thaw the fs.
By this we can limit the damage to minimal, and I hope no one would lose
their data by this anymore.
Suggested-by: Goffredo Baroncelli <kreijack@libero.it>
Link: https://lore.kernel.org/linux-btrfs/83bf3b4b-7f4c-387a-b286-9251e3991e34@bluemole.com/
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 74c30de..bb87b56 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2598,8 +2598,8 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
* 1, 2 2nd and 3rd backup copy
* -1 skip bytenr check
*/
-static int validate_super(struct btrfs_fs_info *fs_info,
- struct btrfs_super_block *sb, int mirror_num)
+int btrfs_validate_super(struct btrfs_fs_info *fs_info,
+ struct btrfs_super_block *sb, int mirror_num)
{
u64 nodesize = btrfs_super_nodesize(sb);
u64 sectorsize = btrfs_super_sectorsize(sb);
@@ -2783,7 +2783,7 @@ static int validate_super(struct btrfs_fs_info *fs_info,
*/
static int btrfs_validate_mount_super(struct btrfs_fs_info *fs_info)
{
- return validate_super(fs_info, fs_info->super_copy, 0);
+ return btrfs_validate_super(fs_info, fs_info->super_copy, 0);
}
/*
@@ -2797,7 +2797,7 @@ static int btrfs_validate_write_super(struct btrfs_fs_info *fs_info,
{
int ret;
- ret = validate_super(fs_info, sb, -1);
+ ret = btrfs_validate_super(fs_info, sb, -1);
if (ret < 0)
goto out;
if (!btrfs_supported_super_csum(btrfs_super_csum_type(sb))) {
@@ -3844,7 +3844,7 @@ static void btrfs_end_super_write(struct bio *bio)
}
struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
- int copy_num)
+ int copy_num, bool drop_cache)
{
struct btrfs_super_block *super;
struct page *page;
@@ -3862,6 +3862,19 @@ struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
if (bytenr + BTRFS_SUPER_INFO_SIZE >= bdev_nr_bytes(bdev))
return ERR_PTR(-EINVAL);
+ if (drop_cache) {
+ /* This should only be called with the primary sb. */
+ ASSERT(copy_num == 0);
+
+ /*
+ * Drop the page of the primary superblock, so later read will
+ * always read from the device.
+ */
+ invalidate_inode_pages2_range(mapping,
+ bytenr >> PAGE_SHIFT,
+ (bytenr + BTRFS_SUPER_INFO_SIZE) >> PAGE_SHIFT);
+ }
+
page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS);
if (IS_ERR(page))
return ERR_CAST(page);
@@ -3893,7 +3906,7 @@ struct btrfs_super_block *btrfs_read_dev_super(struct block_device *bdev)
* later supers, using BTRFS_SUPER_MIRROR_MAX instead
*/
for (i = 0; i < 1; i++) {
- super = btrfs_read_dev_one_super(bdev, i);
+ super = btrfs_read_dev_one_super(bdev, i, false);
if (IS_ERR(super))
continue;
