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
^
Fixes: 1581a884b7ca ("tracing: Remove size restriction on tracing_log_err cmd strings")
Signed-off-by: Zheng Yejian <[email protected]>
---
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
On 2022/11/14 20:46, Masami Hiramatsu (Google) wrote:
> On Mon, 14 Nov 2022 18:46:32 +0800
> Zheng Yejian <[email protected]> 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) <[email protected]>
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 <[email protected]>
>> ---
>> 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
>>
>
>
On Mon, 14 Nov 2022 18:46:32 +0800
Zheng Yejian <[email protected]> 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) <[email protected]>
BTW, I'm interested in how did you reproduce it. Did you inject a memory
allocation failure to reproduce it?
Thank you,
>
> Fixes: 1581a884b7ca ("tracing: Remove size restriction on tracing_log_err cmd strings")
> Signed-off-by: Zheng Yejian <[email protected]>
> ---
> 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
>
--
Masami Hiramatsu (Google) <[email protected]>