From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Pei Xiao <xiaopei01@kylinos.cn>
Cc: joern@lazybastard.org, richard@nod.at, vigneshr@ti.com,
linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
syzbot+b320a4d5f65a61dbbf89@syzkaller.appspotmail.com,
"Jörn Engel" <joern@barelysecure.org>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero
Date: Wed, 12 Aug 2026 14:34:04 +0200 [thread overview]
Message-ID: <871pc3msar.fsf@bootlin.com> (raw)
In-Reply-To: <48230456575d27aa83ce8640de8fc07cc62e8efb.1786499433.git.xiaopei01@kylinos.cn> (Pei Xiao's message of "Wed, 12 Aug 2026 09:52:42 +0800")
On 12/08/2026 at 09:52:42 +08, Pei Xiao <xiaopei01@kylinos.cn> 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@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>
Apparently, removing the cast leads to an unsupported operation with a
64-bit operand on 32-bit architectures (See Sashiko report).
I guess it is best to keep that cast in the end.
Sorry for the changes back-and-forth.
Miquèl
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prev parent reply other threads:[~2026-08-12 12:34 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-12 1:52 [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero Pei Xiao
2026-08-12 12:34 ` Miquel Raynal [this message]
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