On 4/24/21 10:30 PM, Bart Van Assche wrote:

bio_max_size() may get called before device_add_disk() and hence needs to
check whether or not the block device pointer is NULL. Additionally, more
code needs to be modified than __bio_try_merge_page() to limit the bio size
to bio_max_size().

This patch prevents that bio_max_size() triggers the following kernel
crash during a SCSI LUN scan:

BUG: KASAN: null-ptr-deref in bio_add_hw_page+0xa6/0x310
Read of size 8 at addr 00000000000005a8 by task kworker/u16:0/7
Workqueue: events_unbound async_run_entry_fn
Call Trace:
 show_stack+0x52/0x58
 dump_stack+0x9d/0xcf
 kasan_report.cold+0x4b/0x50
 __asan_load8+0x69/0x90
 bio_add_hw_page+0xa6/0x310
 bio_add_pc_page+0xaa/0xe0
 bio_map_kern+0xdc/0x1a0
 blk_rq_map_kern+0xcd/0x2d0
 __scsi_execute+0x9a/0x290 [scsi_mod]
 scsi_probe_lun.constprop.0+0x17c/0x660 [scsi_mod]
 scsi_probe_and_add_lun+0x178/0x750 [scsi_mod]
 __scsi_add_device+0x18c/0x1a0 [scsi_mod]
 ata_scsi_scan_host+0xe5/0x260 [libata]
 async_port_probe+0x94/0xb0 [libata]
 async_run_entry_fn+0x7d/0x2d0
 process_one_work+0x582/0xac0
 worker_thread+0x8f/0x5a0
 kthread+0x222/0x250
 ret_from_fork+0x1f/0x30

This patch also fixes the following kernel warning:

WARNING: CPU: 1 PID: 15449 at block/bio.c:1034
__bio_iov_iter_get_pages+0x324/0x350
Call Trace:
 bio_iov_iter_get_pages+0x6c/0x360
 __blkdev_direct_IO_simple+0x291/0x580
 blkdev_direct_IO+0xb5/0xc0
 generic_file_direct_write+0x10d/0x290
 __generic_file_write_iter+0x120/0x290
 blkdev_write_iter+0x16e/0x280
 new_sync_write+0x268/0x380
 vfs_write+0x3e0/0x4f0
 ksys_write+0xd9/0x180
 __x64_sys_write+0x43/0x50
 do_syscall_64+0x32/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Since I had to shuffle patches anyway, I folded in this fix. Thanks
Bart.

-- 
Jens Axboe