netdev - Re: [PATCH 02/10] bpf: Add multi kprobe link

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Date:   Sun, 6 Mar 2022 18:28:47 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 02/10] bpf: Add multi kprobe link

On Fri, Mar 04, 2022 at 03:11:01PM -0800, Andrii Nakryiko wrote:

SNIP

> > +static int
> > +kprobe_multi_resolve_syms(const void *usyms, u32 cnt,
> > +                         unsigned long *addrs)
> > +{
> > +       unsigned long addr, size;
> > +       const char **syms;
> > +       int err = -ENOMEM;
> > +       unsigned int i;
> > +       char *func;
> > +
> > +       size = cnt * sizeof(*syms);
> > +       syms = kvzalloc(size, GFP_KERNEL);
> > +       if (!syms)
> > +               return -ENOMEM;
> > +
> > +       func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL);
> > +       if (!func)
> > +               goto error;
> > +
> > +       if (copy_from_user(syms, usyms, size)) {
> > +               err = -EFAULT;
> > +               goto error;
> > +       }
> > +
> > +       for (i = 0; i < cnt; i++) {
> > +               err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN);
> > +               if (err == KSYM_NAME_LEN)
> > +                       err = -E2BIG;
> > +               if (err < 0)
> > +                       goto error;
> > +
> > +               err = -EINVAL;
> > +               if (func[0] == '\0')
> > +                       goto error;
> 
> wouldn't empty string be handled by kallsyms_lookup_name?

it would scan and compare all symbols with empty string,
so it's better to test for it

jirka

> 
> > +               addr = kallsyms_lookup_name(func);
> > +               if (!addr)
> > +                       goto error;
> > +               if (!kallsyms_lookup_size_offset(addr, &size, NULL))
> > +                       size = MCOUNT_INSN_SIZE;
> > +               addr = ftrace_location_range(addr, addr + size - 1);
> > +               if (!addr)
> > +                       goto error;
> > +               addrs[i] = addr;
> > +       }
> > +
> > +       err = 0;
> > +error:
> > +       kvfree(syms);
> > +       kfree(func);
> > +       return err;
> > +}
> > +
> 
> [...]