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Date: Mon, 10 Oct 2022 18:34:33 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Xu Kuohai <xukuohai@...wei.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 v3 2/6] libbpf: Fix memory leak in parse_usdt_arg()
On Mon, Oct 10, 2022 at 7:08 AM Xu Kuohai <xukuohai@...wei.com> wrote:
>
> 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 | 59 +++++++++++++++++++++++++-------------------
> 1 file changed, 33 insertions(+), 26 deletions(-)
>
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index e83b497c2245..f3b5be7415b5 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
> @@ -1351,8 +1351,10 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> char *reg_name = NULL;
> int arg_sz, len, reg_off;
> long off;
> + int ret;
>
> - if (sscanf(arg_str, " %d @ \[ %m[a-z0-9], %ld ] %n", &arg_sz, ®_name, &off, &len) == 3) {
> + ret = sscanf(arg_str, " %d @ \[ %m[a-z0-9], %ld ] %n", &arg_sz, ®_name, &off, &len);
> + if (ret == 3) {
> /* Memory dereference case, e.g., -4@[sp, 96] */
> arg->arg_type = USDT_ARG_REG_DEREF;
> arg->val_off = off;
> @@ -1361,32 +1363,37 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> 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, ®_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;
> - } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
> - /* Constant value case, e.g., 4@5 */
> - 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, ®_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;
> } else {
> - pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> - return -EINVAL;
> + if (ret == 2)
> + free(reg_name);
> +
> + if (sscanf(arg_str, " %d @ \[ %m[a-z0-9] ] %n", &arg_sz, ®_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;
> + } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
> + /* Constant value case, e.g., 4@5 */
> + 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, ®_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;
> + } else {
> + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> + return -EINVAL;
> + }
> }
>
I think all this is more complicated than it has to be. How big can
register names be? Few characters? Let's get rid of %m[a-z0-9] and
instead use fixed-max-length strings, e.g., %5s. And read register
names into such local char buffers. It will simplify everything
tremendously. Let's use 16-byte buffers and use %15s to match it?
Would that be enough?
> arg->arg_signed = arg_sz < 0;
> --
> 2.30.2
>
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