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From: Miquel Raynal <miquel.raynal@bootlin.com>
To: "Luca Ceresoli" <luca.ceresoli@bootlin.com>
Cc: "Dan Carpenter" <error27@gmail.com>,
	 "Harshit Mogalapalli" <harshit.m.mogalapalli@oracle.com>,
	 "Richard Weinberger" <richard@nod.at>,
	 "Vignesh Raghavendra" <vigneshr@ti.com>,
	 "Amit Kumar Mahapatra" <amit.kumar-mahapatra@amd.com>,
	<linux-mtd@lists.infradead.org>,  <linux-kernel@vger.kernel.org>,
	<kernel-janitors@vger.kernel.org>
Subject: Re: [PATCH] mtd: virt_concat: fix use-after-free in mtd_virt_concat_destroy_joins()
Date: Mon, 22 Jun 2026 09:32:43 +0200	[thread overview]
Message-ID: <874iiv3u90.fsf@bootlin.com> (raw)
In-Reply-To: <DJARC89F2VJR.1EDEQ27GSDAK6@bootlin.com> (Luca Ceresoli's message of "Tue, 16 Jun 2026 22:31:28 +0200")

On 16/06/2026 at 22:31:28 +02, "Luca Ceresoli" <luca.ceresoli@bootlin.com> wrote:

> On Tue Jun 16, 2026 at 12:13 PM CEST, Dan Carpenter wrote:
>> On Tue, Jun 16, 2026 at 11:51:53AM +0200, Luca Ceresoli wrote:

Yes, container_of() for issue 1 seems to be a better approach.

>>> Issue 2: in mtd_virt_concat_destroy_joins():
>>>
>>> 	list_for_each_entry_safe(item, tmp, &concat_node_list, head) {
>>> 		mtd = &item->concat->mtd; [0]
>>> 		if (item->concat) { [1]
>>>
>>> At line [0] we dereference item->concat, but at line [1] we apparently
>>> handle the case where item->concat can be NULL. Either [1] is always true
>>> and we can remove the if(), or [1] can be false, so [0] is a bug and should
>>> probably be moved to inside the if().
>>
>> That's not a dereference on line 0, it's pointer math.  So the code
>> works.  But a lot of people find the distinction confusing.
>
> Ah, indeed, you are right on both aspects: it's just pointer math (not a
> bug) + it is confusing code.
>
> So moving [0] inside the if() would be a readability improvement IMO, but
> definitely not a bugfix.

Yes!

Thanks,
Miquèl

WARNING: multiple messages have this Message-ID (diff)
From: Miquel Raynal <miquel.raynal@bootlin.com>
To: "Luca Ceresoli" <luca.ceresoli@bootlin.com>
Cc: "Dan Carpenter" <error27@gmail.com>,
	 "Harshit Mogalapalli" <harshit.m.mogalapalli@oracle.com>,
	 "Richard Weinberger" <richard@nod.at>,
	 "Vignesh Raghavendra" <vigneshr@ti.com>,
	 "Amit Kumar Mahapatra" <amit.kumar-mahapatra@amd.com>,
	<linux-mtd@lists.infradead.org>,  <linux-kernel@vger.kernel.org>,
	<kernel-janitors@vger.kernel.org>
Subject: Re: [PATCH] mtd: virt_concat: fix use-after-free in mtd_virt_concat_destroy_joins()
Date: Mon, 22 Jun 2026 09:32:43 +0200	[thread overview]
Message-ID: <874iiv3u90.fsf@bootlin.com> (raw)
In-Reply-To: <DJARC89F2VJR.1EDEQ27GSDAK6@bootlin.com> (Luca Ceresoli's message of "Tue, 16 Jun 2026 22:31:28 +0200")

On 16/06/2026 at 22:31:28 +02, "Luca Ceresoli" <luca.ceresoli@bootlin.com> wrote:

> On Tue Jun 16, 2026 at 12:13 PM CEST, Dan Carpenter wrote:
>> On Tue, Jun 16, 2026 at 11:51:53AM +0200, Luca Ceresoli wrote:

Yes, container_of() for issue 1 seems to be a better approach.

>>> Issue 2: in mtd_virt_concat_destroy_joins():
>>>
>>> 	list_for_each_entry_safe(item, tmp, &concat_node_list, head) {
>>> 		mtd = &item->concat->mtd; [0]
>>> 		if (item->concat) { [1]
>>>
>>> At line [0] we dereference item->concat, but at line [1] we apparently
>>> handle the case where item->concat can be NULL. Either [1] is always true
>>> and we can remove the if(), or [1] can be false, so [0] is a bug and should
>>> probably be moved to inside the if().
>>
>> That's not a dereference on line 0, it's pointer math.  So the code
>> works.  But a lot of people find the distinction confusing.
>
> Ah, indeed, you are right on both aspects: it's just pointer math (not a
> bug) + it is confusing code.
>
> So moving [0] inside the if() would be a readability improvement IMO, but
> definitely not a bugfix.

Yes!

Thanks,
Miquèl

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2026-06-22  7:32 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-06-14  8:10 [PATCH] mtd: virt_concat: fix use-after-free in mtd_virt_concat_destroy_joins() Harshit Mogalapalli
2026-06-14  8:10 ` Harshit Mogalapalli
2026-06-16  9:51 ` Luca Ceresoli
2026-06-16  9:51   ` Luca Ceresoli
2026-06-16 10:13   ` Dan Carpenter
2026-06-16 10:13     ` Dan Carpenter
2026-06-16 20:31     ` Luca Ceresoli
2026-06-16 20:31       ` Luca Ceresoli
2026-06-22  7:32       ` Miquel Raynal [this message]
2026-06-22  7:32         ` Miquel Raynal
2026-06-16 12:25 ` Harshit Mogalapalli
2026-06-16 12:25   ` Harshit Mogalapalli

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