Re: RFC PATCH] null_blk: fix UBSAN shift-out-of-bounds when zone_size is 0 or overflows

On Sat, 08 Aug 2026 11:42:39 -0400, Rik van Riel wrote:
> null_zone_no() does sect >> ilog2(dev->zone_size_sects). When
> zone_size_sects is 0, ilog2(0) returns -1, producing shift exponent -1
> which UBSAN reports as shift-out-of-bounds.
> 
>   UBSAN: shift-out-of-bounds in drivers/block/null_blk/zoned.c:21:14
>   shift exponent -1 is negative
>   Call Trace:
>    null_zone_no drivers/block/null_blk/zoned.c:21 [inline]
>    null_process_zoned_cmd+0xf76/0xf80 drivers/block/null_blk/zoned.c:728
>    null_handle_cmd drivers/block/null_blk/main.c:1455 [inline]
>    null_queue_rq+0x8bc/0xe70 drivers/block/null_blk/main.c:1703
>    __blk_mq_issue_directly block/blk-mq.c:2694 [inline]
>    blk_mq_try_issue_directly+0x3f4/0x880 block/blk-mq.c:2754
>    blk_mq_submit_bio+0x20c0/0x2a40 block/blk-mq.c:3208
>    submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:790
>    block_read_full_folio+0x7a6/0x810 fs/buffer.c:2463
>    filemap_read_folio+0x12c/0x3a0 mm/filemap.c:2510
>    read_part_sector+0xb6/0x2b0 block/partitions/core.c:724
>    adfspart_check_ICS+0xb1/0x960 block/partitions/acorn.c:357
>    check_partition block/partitions/core.c:143 [inline]
>    blk_add_partitions block/partitions/core.c:591 [inline]
>    bdev_disk_changed+0x851/0x17a0 block/partitions/core.c:695
>    blkdev_get_whole+0x372/0x510 block/bdev.c:751
>    add_disk_final block/genhd.c:412 [inline]
>    add_disk_fwnode+0x24b/0x3a0 block/genhd.c:606
>    null_add_dev+0x130b/0x1d70 drivers/block/null_blk/main.c:2052
>    nullb_device_power_store+0x240/0x380 drivers/block/null_blk/main.c:501
>    configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
> 
> [...]

Applied, thanks!

[1/1] RFC PATCH] null_blk: fix UBSAN shift-out-of-bounds when zone_size is 0 or overflows
      commit: 95491fb05105b61050cb623a5e0227eb26aa3525

Best regards,
-- 
Jens Axboe