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

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

[Pei Xiao]

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@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/6a7b58ba.ac361c09.22ff0a.0045.GAE@google.com/
Suggested-by: Jörn Engel <joern@barelysecure.org>
Cc: stable@vger.kernel.org
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
changes in v3:
1.remove (long) cast due to build errors in 32bit config systems
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;
 	}
-- 
2.25.1

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@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/lkml/6a7b58ba.ac361c09.22ff0a.0045.GAE@google.com/
> Suggested-by: Jörn Engel <joern@barelysecure.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
> ---
> 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;
>  	}

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@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/lkml/6a7b58ba.ac361c09.22ff0a.0045.GAE@google.com/
> Suggested-by: Jörn Engel <joern@barelysecure.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Add cc Maintainers.
> ---
> changes in v3:
> 1.remove (long) cast due to build errors in 32bit config systems
> 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;
>  	}

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

[Miquel Raynal]

On Thu, 13 Aug 2026 10:48:12 +0800, Pei Xiao 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:
> 
> [...]

Applied to mtd/fixes, thanks!

[1/1] mtd: block2mtd: Fix divide error when erase_size is zero
      commit: b5965c4221165045e19736794ca5f48ae3d67142

Patche(s) should be available on mtd/linux.git and will be
part of the next PR (provided that no robot complains by then).

Kind regards,
Miquèl