* [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero
@ 2026-08-12 1:52 ` Pei Xiao
0 siblings, 0 replies; 4+ messages in thread
From: Pei Xiao @ 2026-08-12 1:52 UTC (permalink / raw)
To: joern, miquel.raynal, richard, vigneshr, linux-mtd, linux-kernel
Cc: Pei Xiao, syzbot+b320a4d5f65a61dbbf89, Jörn Engel, stable
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>
---
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..3e2367dfff88 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 || size % erase_size) {
pr_err("erasesize must be a divisor of device size\n");
goto err_free_block2mtd;
}
--
2.25.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero
@ 2026-08-12 1:52 ` Pei Xiao
0 siblings, 0 replies; 4+ messages in thread
From: Pei Xiao @ 2026-08-12 1:52 UTC (permalink / raw)
To: joern, miquel.raynal, richard, vigneshr, linux-mtd, linux-kernel
Cc: Pei Xiao, syzbot+b320a4d5f65a61dbbf89, Jörn Engel, stable
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>
---
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..3e2367dfff88 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 || size % erase_size) {
pr_err("erasesize must be a divisor of device size\n");
goto err_free_block2mtd;
}
--
2.25.1
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero
2026-08-12 1:52 ` Pei Xiao
@ 2026-08-12 12:34 ` Miquel Raynal
-1 siblings, 0 replies; 4+ messages in thread
From: Miquel Raynal @ 2026-08-12 12:34 UTC (permalink / raw)
To: Pei Xiao
Cc: joern, richard, vigneshr, linux-mtd, linux-kernel,
syzbot+b320a4d5f65a61dbbf89, Jörn Engel, stable
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
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero
@ 2026-08-12 12:34 ` Miquel Raynal
0 siblings, 0 replies; 4+ messages in thread
From: Miquel Raynal @ 2026-08-12 12:34 UTC (permalink / raw)
To: Pei Xiao
Cc: joern, richard, vigneshr, linux-mtd, linux-kernel,
syzbot+b320a4d5f65a61dbbf89, Jörn Engel, stable
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
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-08-12 12:34 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-08-12 1:52 [PATCH v2] mtd: block2mtd: Fix divide error when erase_size is zero Pei Xiao
2026-08-12 1:52 ` Pei Xiao
2026-08-12 12:34 ` Miquel Raynal
2026-08-12 12:34 ` Miquel Raynal
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