Re: [PATCH bpf-next v4 2/6] libbpf: Fix memory leak in parse_usdt_arg()

[Xu Kuohai <xukuohai@huawei.com>]

On 10/13/2022 11:47 PM, Andrii Nakryiko wrote:
> On Tue, Oct 11, 2022 at 4:43 AM Xu Kuohai <xukuohai@huaweicloud.com> wrote:
>>
>> From: Xu Kuohai <xukuohai@huawei.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@huawei.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
>>
> .