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bcache: check and adjust logical block size for backing devices

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It's possible for a block driver to set logical block size to
a value greater than page size incorrectly; e.g. bcache takes
the value from the superblock, set by the user w/ make-bcache.

This causes a BUG/NULL pointer dereference in the path:

  __blkdev_get()
  -> set_init_blocksize() // set i_blkbits based on ...
     -> bdev_logical_block_size()
        -> queue_logical_block_size() // ... this value
  -> bdev_disk_changed()
     ...
     -> blkdev_readpage()
        -> block_read_full_page()
           -> create_page_buffers() // size = 1 << i_blkbits
              -> create_empty_buffers() // give size/take pointer
                 -> alloc_page_buffers() // return NULL
                 .. BUG!

Because alloc_page_buffers() is called with size > PAGE_SIZE,
thus it initializes head = NULL, skips the loop, return head;
then create_empty_buffers() gets (and uses) the NULL pointer.

This has been around longer than commit ad6bf88a6c ("block:
fix an integer overflow in logical block size"); however, it
increased the range of values that can trigger the issue.

Previously only 8k/16k/32k (on x86/4k page size) would do it,
as greater values overflow unsigned short to zero, and queue_
logical_block_size() would then use the default of 512.

Now the range with unsigned int is much larger, and users w/
the 512k value, which happened to be zero'ed previously and
work fine, started to hit this issue -- as the zero is gone,
and queue_logical_block_size() does return 512k (>PAGE_SIZE.)

Fix this by checking the bcache device's logical block size,
and if it's greater than page size, fallback to the backing/
cached device's logical page size.

This doesn't affect cache devices as those are still checked
for block/page size in read_super(); only the backing/cached
devices are not.

Apparently it's a regression from commit 2903381fce ("bcache:
Take data offset from the bdev superblock."), moving the check
into BCACHE_SB_VERSION_CDEV only. Now that we have superblocks
of backing devices out there with this larger value, we cannot
refuse to load them (i.e., have a similar check in _BDEV.)

Ideally perhaps bcache should use all values from the backing
device (physical/logical/io_min block size)? But for now just
fix the problematic case.

Test-case:

    # IMG=/root/disk.img
    # dd if=/dev/zero of=$IMG bs=1 count=0 seek=1G
    # DEV=$(losetup --find --show $IMG)
    # make-bcache --bdev $DEV --block 8k
      < see dmesg >

Before:

    # uname -r
    5.7.0-rc7

    [   55.944046] BUG: kernel NULL pointer dereference, address: 0000000000000000
    ...
    [   55.949742] CPU: 3 PID: 610 Comm: bcache-register Not tainted 5.7.0-rc7 #4
    ...
    [   55.952281] RIP: 0010:create_empty_buffers+0x1a/0x100
    ...
    [   55.966434] Call Trace:
    [   55.967021]  create_page_buffers+0x48/0x50
    [   55.967834]  block_read_full_page+0x49/0x380
    [   55.972181]  do_read_cache_page+0x494/0x610
    [   55.974780]  read_part_sector+0x2d/0xaa
    [   55.975558]  read_lba+0x10e/0x1e0
    [   55.977904]  efi_partition+0x120/0x5a6
    [   55.980227]  blk_add_partitions+0x161/0x390
    [   55.982177]  bdev_disk_changed+0x61/0xd0
    [   55.982961]  __blkdev_get+0x350/0x490
    [   55.983715]  __device_add_disk+0x318/0x480
    [   55.984539]  bch_cached_dev_run+0xc5/0x270
    [   55.986010]  register_bcache.cold+0x122/0x179
    [   55.987628]  kernfs_fop_write+0xbc/0x1a0
    [   55.988416]  vfs_write+0xb1/0x1a0
    [   55.989134]  ksys_write+0x5a/0xd0
    [   55.989825]  do_syscall_64+0x43/0x140
    [   55.990563]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
    [   55.991519] RIP: 0033:0x7f7d60ba3154
    ...

After:

    # uname -r
    5.7.0.bcachelbspgsz

    [   31.672460] bcache: bcache_device_init() bcache0: sb/logical block size (8192) greater than page size (4096) falling back to device logical block size (512)
    [   31.675133] bcache: register_bdev() registered backing device loop0

    # grep ^ /sys/block/bcache0/queue/*_block_size
    /sys/block/bcache0/queue/logical_block_size:512
    /sys/block/bcache0/queue/physical_block_size:8192

Reported-by: Ryan Finnie <ryan@finnie.org>
Reported-by: Sebastian Marsching <sebastian@marsching.com>
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Mauricio Faria de Oliveira 2020-06-15 00:53:31 +08:00 committed by Jens Axboe
parent be23e83733
commit dcacbc1242
1 changed files with 19 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
drivers/md/bcache/super.c
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@ -819,7 +819,8 @@ static void bcache_device_free(struct bcache_device *d)
}
static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
sector_t sectors, make_request_fn make_request_fn)
sector_t sectors, make_request_fn make_request_fn,
struct block_device *cached_bdev)
{
struct request_queue *q;
const size_t max_stripes = min_t(size_t, INT_MAX,
@ -885,6 +886,21 @@ static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
q->limits.io_min = block_size;
q->limits.logical_block_size = block_size;
q->limits.physical_block_size = block_size;
if (q->limits.logical_block_size > PAGE_SIZE && cached_bdev) {
/*
* This should only happen with BCACHE_SB_VERSION_BDEV.
* Block/page size is checked for BCACHE_SB_VERSION_CDEV.
*/
pr_info("%s: sb/logical block size (%u) greater than page size "
"(%lu) falling back to device logical block size (%u)",
d->disk->disk_name, q->limits.logical_block_size,
PAGE_SIZE, bdev_logical_block_size(cached_bdev));
/* This also adjusts physical block size/min io size if needed */
blk_queue_logical_block_size(q, bdev_logical_block_size(cached_bdev));
}
blk_queue_flag_set(QUEUE_FLAG_NONROT, d->disk->queue);
blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, d->disk->queue);
blk_queue_flag_set(QUEUE_FLAG_DISCARD, d->disk->queue);
@ -1340,7 +1356,7 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
ret = bcache_device_init(&dc->disk, block_size,
dc->bdev->bd_part->nr_sects - dc->sb.data_offset,
cached_dev_make_request);
cached_dev_make_request, dc->bdev);
if (ret)
return ret;
@ -1453,7 +1469,7 @@ static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)
kobject_init(&d->kobj, &bch_flash_dev_ktype);
if (bcache_device_init(d, block_bytes(c), u->sectors,
flash_dev_make_request))
flash_dev_make_request, NULL))
goto err;
bcache_device_attach(d, c, u - c->uuids);