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Message-ID: <d0a3ea62-e600-483c-a5d5-4584b9e464dd@huawei.com>
Date: Mon, 14 Nov 2022 21:06:57 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
CC: <rostedt@...dmis.org>, <linux-kernel@...r.kernel.org>,
<linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: Fix potential null-pointer-access of entry in
list 'tr->err_log'
On 2022/11/14 20:46, Masami Hiramatsu (Google) wrote:
> On Mon, 14 Nov 2022 18:46:32 +0800
> Zheng Yejian <zhengyejian1@...wei.com> wrote:
>
>> Entries in list 'tr->err_log' will be reused after entry number
>> exceed TRACING_LOG_ERRS_MAX.
>>
>> The cmd string of the to be reused entry will be freed first then
>> allocated a new one. If the allocation failed, then the entry will
>> still be in list 'tr->err_log' but its 'cmd' field is set to be NULL,
>> later access of 'cmd' is risky.
>>
>> Currently above problem can cause the loss of 'cmd' information of first
>> entry in 'tr->err_log'. When execute `cat /sys/kernel/tracing/error_log`,
>> reproduce logs like:
>> [ 37.495100] trace_kprobe: error: Maxactive is not for kprobe(null) ^
>> [ 38.412517] trace_kprobe: error: Maxactive is not for kprobe
>> Command: p4:myprobe2 do_sys_openat2
>> ^
>
> This looks good to me.
>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thanks!
>
> BTW, I'm interested in how did you reproduce it. Did you inject a memory
> allocation failure to reproduce it?
Yes. I happended to find this problem when I was looking at the code,
then I inject an allocation failure to proof it.
>
> Thank you,
>
>>
>> Fixes: 1581a884b7ca ("tracing: Remove size restriction on tracing_log_err cmd strings")
>> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
>> ---
>> kernel/trace/trace.c | 9 +++++----
>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 47a44b055a1d..5ae776598106 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -7802,6 +7802,7 @@ static struct tracing_log_err *get_tracing_log_err(struct trace_array *tr,
>> int len)
>> {
>> struct tracing_log_err *err;
>> + char *cmd;
>>
>> if (tr->n_err_log_entries < TRACING_LOG_ERRS_MAX) {
>> err = alloc_tracing_log_err(len);
>> @@ -7810,12 +7811,12 @@ static struct tracing_log_err *get_tracing_log_err(struct trace_array *tr,
>>
>> return err;
>> }
>> -
>> + cmd = kzalloc(len, GFP_KERNEL);
>> + if (!cmd)
>> + return ERR_PTR(-ENOMEM);
>> err = list_first_entry(&tr->err_log, struct tracing_log_err, list);
>> kfree(err->cmd);
>> - err->cmd = kzalloc(len, GFP_KERNEL);
>> - if (!err->cmd)
>> - return ERR_PTR(-ENOMEM);
>> + err->cmd = cmd;
>> list_del(&err->list);
>>
>> return err;
>> --
>> 2.25.1
>>
>
>
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