1. 09 Aug, 2020 12 commits
  2. 20 Jul, 2020 3 commits
  3. 17 Jul, 2020 1 commit
    • Mauricio Faria de Oliveira's avatar
      bcache: check and adjust logical block size for backing devices · a277f856
      Mauricio Faria de Oliveira authored
      BugLink: https://bugs.launchpad.net/bugs/1867916
      
      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 ad6bf88a ("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 2903381f ("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: default avatarRyan Finnie <ryan@finnie.org>
      Reported-by: default avatarSebastian Marsching <sebastian@marsching.com>
      Signed-off-by: default avatarMauricio Faria de Oliveira <mfo@canonical.com>
      Signed-off-by: default avatarColy Li <colyli@suse.de>
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      (backported from commit dcacbc12)
      [mfo: backport: hunks 1/3/4: adjust bcache_device_init() signature
       and calls for the lack of parameter make_request_fn from upstream.
       hunk 1: adjust bcache_device_init() signature for 'unsigned (int)',
               and refresh one context line.
       hunk 2: change from blk_queue_flag_set/clear() to set/clear_bit().]
      Signed-off-by: default avatarMauricio Faria de Oliveira <mfo@canonical.com>
      Acked-by: default avatarAndrea Righi <andrea.righi@canonical.com>
      Acked-by: default avatarStefan Bader <stefan.bader@canonical.com>
      Signed-off-by: default avatarKelsey Skunberg <kelsey.skunberg@canonical.com>
      a277f856
  4. 14 Jul, 2020 24 commits