Re: [PATCH v3] mtd: block2mtd: Fix divide error when erase_size is zero

[Pei Xiao]

在 2026/8/13 10:48, Pei Xiao 写道:
> The erase size is parsed from the "block2mtd" module parameter and can
> be set to zero. add_device() then evaluates
> 
>         if (size % erase_size)
> 
> with a zero divisor, which triggers a divide error:
> 
> divide error: 0000 [#1] PREEMPT SMP PTI
> RIP: 0010:add_device drivers/mtd/devices/block2mtd.c:296 [inline]
> RIP: 0010:block2mtd_setup2+0x592/0xda0 drivers/mtd/devices/block2mtd.c:459
> Call Trace:
> block2mtd_setup+0x27/0xe0 drivers/mtd/devices/block2mtd.c:476
> param_attr_store+0x214/0x310 kernel/params.c:589
> module_attr_store+0x65/0x90 kernel/params.c:904
> kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
> ...
> 
> Reject a zero erase size before performing the modulo operation so the
> existing "erasesize must be a divisor of device size" error path
> reports the invalid argument and frees the device.
> 
> Fixes: ea6d833a3fdd ("mtd: block2mtd: check device size")
> Reported-by: syzbot+b320a4d5f65a61dbbf89@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/lkml/6a7b58ba.ac361c09.22ff0a.0045.GAE@xxxxxxxxxx/
> Suggested-by: Jörn Engel <joern@xxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
> ---
> changes in v3:
> 1.remove (long) cast due to build errors in 32bit config systems
Add.
> 2.changes git log about (long) cast
> 
> changlogs in v2:
> 1.Add Suggested-by tag
> 2.remove unnecessary (long) cast from the size
> ---
>  drivers/mtd/devices/block2mtd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
> index 03e80b2c4f5a..349fa07be314 100644
> --- a/drivers/mtd/devices/block2mtd.c
> +++ b/drivers/mtd/devices/block2mtd.c
> @@ -293,7 +293,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
>  	}
>  
>  	size = bdev_nr_bytes(bdev);
> -	if ((long)size % erase_size) {
> +	if (!erase_size || (long)size % erase_size) {
>  		pr_err("erasesize must be a divisor of device size\n");
>  		goto err_free_block2mtd;
>  	}