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Message-ID: <02741f84-ee8f-2f4c-e2eb-5f74183f60f8@kernel.org>
Date:   Tue, 29 Mar 2022 08:07:16 +0200
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Subject: Re: [PATCH v3] char: tty3270: fix a missing check on list iterator
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To:     Xiaomeng Tong <xiam0nd.tong@gmail.com>
Cc:     agordeev@linux.ibm.com, borntraeger@linux.ibm.com,
        dsterba@suse.com, elder@linaro.org, gor@linux.ibm.com,
        gregkh@linuxfoundation.org, hca@linux.ibm.com, jcmvbkbc@gmail.com,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        stable@vger.kernel.org, svens@linux.ibm.com
References: <47a6e396-3d51-79f5-a544-8942470fa2fd@kernel.org>
 <20220328102732.28910-1-xiam0nd.tong@gmail.com>
From:   Jiri Slaby <jirislaby@kernel.org>
In-Reply-To: <20220328102732.28910-1-xiam0nd.tong@gmail.com>
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On 28. 03. 22, 12:27, Xiaomeng Tong wrote:
> On Mon, 28 Mar 2022 12:09:59 +0200, Jiri Slaby wrote:
>> On 28. 03. 22, 11:35, Xiaomeng Tong wrote:
>>> The bug is here:
>>> 	if (s->len != flen) {
>>>
>>> The list iterator 's' will point to a bogus position containing
>>> HEAD if the list is empty or no element is found.
>>
>> Could you also explain how that can happen?
>>
> 
> When list_for_each_entry_* do not early exits (if the list is empty
> or no break/goto/return hit inside the loop), it will set pos ('s' here)
> with a bogus pointer that point to a invalid struct computed based
> on &HEAD using container_of.
> 
> #define list_for_each_entry(pos, head, member)                          \
>          for (pos = list_first_entry(head, typeof(*pos), member);        \
>               !list_entry_is_head(pos, head, member);                    \
>               pos = list_next_entry(pos, member))

No, I didn't mean what happens on that site on the code level. I think 
everyone understands that. Instead, I meant: what circumstances lead to 
this _situation_ in reality?

thanks,
-- 
js
suse labs