[PATCH] powerpc/pseries/hotplug-cpu: Fix memleak when cpus node not exist

[Michael Ellerman]

Tyrel Datwyler <tyreld at linux.ibm.com> writes:
> On 11/10/20 6:08 AM, Nathan Lynch wrote:
>> Zhang Xiaoxu <zhangxiaoxu5 at huawei.com> writes:
>>> From: zhangxiaoxu <zhangxiaoxu5 at huawei.com>
>>>
>>> If the cpus nodes not exist, we lost to free the 'cpu_drcs', which
>>> will leak memory.
>>>
>>> Fixes: a0ff72f9f5a7 ("powerpc/pseries/hotplug-cpu: Remove double free in error path")
>>> Reported-by: Hulk Robot <hulkci at huawei.com>
>>> Signed-off-by: zhangxiaoxu <zhangxiaoxu5 at huawei.com>
>>> ---
>>>  arch/powerpc/platforms/pseries/hotplug-cpu.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
>>> index f2837e33bf5d..4bb1c9f2bb11 100644
>>> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
>>> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
>>> @@ -743,6 +743,7 @@ static int dlpar_cpu_add_by_count(u32 cpus_to_add)
>>>  	parent = of_find_node_by_path("/cpus");
>>>  	if (!parent) {
>>>  		pr_warn("Could not find CPU root node in device tree\n");
>>> +		kfree(cpu_drcs);
>>>  		return -1;
>>>  	}
>> 
>> Thanks for finding this.
>> 
>> a0ff72f9f5a7 ("powerpc/pseries/hotplug-cpu: Remove double free in error
>> path") was posted in Sept 2019 but was not applied until July 2020:
>> 
>> https://lore.kernel.org/linuxppc-dev/20190919231633.1344-1-nathanl@linux.ibm.com/
>> 
>> Here is that change as posted; note the function context is
>> find_dlpar_cpus_to_add(), not dlpar_cpu_add_by_count():
>> 
>> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
>> @@ -726,7 +726,6 @@ static int find_dlpar_cpus_to_add(u32 *cpu_drcs, u32 cpus_to_add)
>>  	parent = of_find_node_by_path("/cpus");
>>  	if (!parent) {
>>  		pr_warn("Could not find CPU root node in device tree\n");
>> -		kfree(cpu_drcs);
>>  		return -1;
>>  	}
>> 
>> Meanwhile b015f6bc9547dbc056edde7177c7868ca8629c4c ("powerpc/pseries: Add
>> cpu DLPAR support for drc-info property") was posted in Nov 2019 and
>> committed a few days later:
>> 
>> https://lore.kernel.org/linux-pci/1573449697-5448-4-git-send-email-tyreld@linux.ibm.com/
>> 
>> This change reorganized the same code, removing
>> find_dlpar_cpus_to_add(), and it had the effect of fixing the same
>> issue.
>> 
>> However git apparently allowed the older change to still apply on top of
>> this (changing a function different from the one in the original
>> patch!), leading to a real bug.
>
> Yikes, not sure how that happened without either the committer massaging the
> patch to apply, or the line location and context matching exactly.

git-am won't apply it, but patch does. I often have to fall back to
using patch when things don't apply, so that's presumably what happened
here. I try to manually check the result is correct but I obviously
didn't do a good job here.

cheers