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

[Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>]

On Tue, Oct 11, 2022 at 4:43 AM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:
>
> From: Xu Kuohai <xukuohai@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
>  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.


>                 /* 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
>