Re: [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero

[Pei Xiao]

在 2026/8/12 20:34, Miquel Raynal 写道:
> On 12/08/2026 at 09:52:42 +08, Pei Xiao <xiaopei01@xxxxxxxxxx> wrote:
> 
>> 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.
>>
>> While at it, drop the unnecessary (long) cast from the size operand of
>> the modulo.
>>
>> 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>
> 
> Apparently, removing the cast leads to an unsupported operation with a
> 64-bit operand on 32-bit architectures (See Sashiko report).
Using i386 for testing does reveal compilation issues; I will retain
this (long) cast and send the third version of the patch.

make ARCH=i386 -j$(nproc)

ld: drivers/mtd/devices/block2mtd.o: in function `block2mtd_setup2':
block2mtd.c:(.text+0x315): undefined reference to `__moddi3'
make[2]: *** [scripts/Makefile.vmlinux:72：vmlinux.unstripped] 错误 1

> 
> I guess it is best to keep that cast in the end.
> 
> Sorry for the changes back-and-forth.
It is my pleasure.

Pei.
> 
> Miquèl