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Date: Tue, 11 Oct 2022 14:26:33 +0800
From: Xu Kuohai <xukuohai@...wei.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.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 10/11/2022 9:34 AM, Andrii Nakryiko wrote:
> 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?
>
The valid register names accepted by calc_pt_regs_off() are x0~x31 and sp, so
16-byte buffer is enough. Since %15s matches all non-space characters, will use
%15[a-z0-9] to match it.
>> arg->arg_signed = arg_sz < 0;
>> --
>> 2.30.2
>>
> .
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