linux-kernel - Re: [PATCH bpf-next v4 2/6] libbpf: Fix memory leak in parse_usdt

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Message-ID: <86c88c01-22eb-b7f8-9c65-0faf97b4096b@huawei.com>
Date:   Fri, 14 Oct 2022 09:53:23 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Xu Kuohai <xukuohai@...weicloud.com>
CC:     <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Delyan Kratunov <delyank@...com>,
        Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH bpf-next v4 2/6] libbpf: Fix memory leak in
 parse_usdt_arg()

On 10/13/2022 11:47 PM, Andrii Nakryiko wrote:
> On Tue, Oct 11, 2022 at 4:43 AM Xu Kuohai <xukuohai@...weicloud.com> wrote:
>>
>> From: Xu Kuohai <xukuohai@...wei.com>
>>
>> In the arm64 version of parse_usdt_arg(), when sscanf returns 2, reg_name
>> is allocated but not freed. Fix it.
>>
>> Fixes: 0f8619929c57 ("libbpf: Usdt aarch64 arg parsing support")
>> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
>> ---
>>   tools/lib/bpf/usdt.c | 11 ++++-------
>>   1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
>> index e83b497c2245..49f3c3b7f609 100644
>> --- a/tools/lib/bpf/usdt.c
>> +++ b/tools/lib/bpf/usdt.c
>> @@ -1348,25 +1348,23 @@ static int calc_pt_regs_off(const char *reg_name)
>>
>>   static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
>>   {
>> -       char *reg_name = NULL;
>> +       char reg_name[16];
>>          int arg_sz, len, reg_off;
>>          long off;
>>
>> -       if (sscanf(arg_str, " %d @ \[ %m[a-z0-9], %ld ] %n", &arg_sz, &reg_name, &off, &len) == 3) {
>> +       if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], %ld ] %n", &arg_sz, reg_name, &off, &len) == 3) {
> 
> It would be nice to do the same change for other architectures where
> it makes sense and avoid having to deal with unnecessary memory
> allocations. Please send follow up patches with similar changes for
> other implementations of parse_usdt_arg. Thanks.
>

ok, will do

> 
>>                  /* Memory dereference case, e.g., -4@[sp, 96] */
>>                  arg->arg_type = USDT_ARG_REG_DEREF;
>>                  arg->val_off = off;
>>                  reg_off = calc_pt_regs_off(reg_name);
>> -               free(reg_name);
>>                  if (reg_off < 0)
>>                          return reg_off;
>>                  arg->reg_off = reg_off;
>> -       } else if (sscanf(arg_str, " %d @ \[ %m[a-z0-9] ] %n", &arg_sz, &reg_name, &len) == 2) {
>> +       } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
>>                  /* Memory dereference case, e.g., -4@[sp] */
>>                  arg->arg_type = USDT_ARG_REG_DEREF;
>>                  arg->val_off = 0;
>>                  reg_off = calc_pt_regs_off(reg_name);
>> -               free(reg_name);
>>                  if (reg_off < 0)
>>                          return reg_off;
>>                  arg->reg_off = reg_off;
>> @@ -1375,12 +1373,11 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
>>                  arg->arg_type = USDT_ARG_CONST;
>>                  arg->val_off = off;
>>                  arg->reg_off = 0;
>> -       } else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) {
>> +       } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
>>                  /* Register read case, e.g., -8@x4 */
>>                  arg->arg_type = USDT_ARG_REG;
>>                  arg->val_off = 0;
>>                  reg_off = calc_pt_regs_off(reg_name);
>> -               free(reg_name);
>>                  if (reg_off < 0)
>>                          return reg_off;
>>                  arg->reg_off = reg_off;
>> --
>> 2.30.2
>>
> .