Re: [PATCH v1] perf llvm: Fix inadvertent file creation

[Ian Rogers]

On Thu, Jan 5, 2023 at 12:26 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> The LLVM template is first echo-ed into command_out and then
> command_out executed. The echo surrounds the template with double
> quotes, however, the template itself may contain quotes. This is
> generally innocuous but in tools/perf/tests/bpf-script-test-prologue.c
> we see:
> ...
> SEC("func=null_lseek file->f_mode offset orig")
> ...
> where the first double quote ends the double quote of the echo, then
> the > redirects output into a file called f_mode.
>
> To avoid this inadvertent behavior substitute redirects and similar
> characters to be ASCII control codes, then substitute the output in
> the echo back again.
>
> Fixes: 5eab5a7ee032 ("perf llvm: Display eBPF compiling command in debug output")
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

Ping. Not really a BPF/LLVM fix, it is just doing some string
manipulation to avoid shell interpretation in the context of making
BPF/LLVM.

Thanks,
Ian

> ---
>  tools/perf/util/llvm-utils.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
> index 650ffe336f3a..4e8e243a6e4b 100644
> --- a/tools/perf/util/llvm-utils.c
> +++ b/tools/perf/util/llvm-utils.c
> @@ -531,14 +531,37 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
>
>         pr_debug("llvm compiling command template: %s\n", template);
>
> +       /*
> +        * Below, substitute control characters for values that can cause the
> +        * echo to misbehave, then substitute the values back.
> +        */
>         err = -ENOMEM;
> -       if (asprintf(&command_echo, "echo -n \"%s\"", template) < 0)
> +       if (asprintf(&command_echo, "echo -n \a%s\a", template) < 0)
>                 goto errout;
>
> +#define SWAP_CHAR(a, b) do { if (*p == a) *p = b; } while (0)
> +       for (char *p = command_echo; *p; p++) {
> +               SWAP_CHAR('<', '\001');
> +               SWAP_CHAR('>', '\002');
> +               SWAP_CHAR('"', '\003');
> +               SWAP_CHAR('\'', '\004');
> +               SWAP_CHAR('|', '\005');
> +               SWAP_CHAR('&', '\006');
> +               SWAP_CHAR('\a', '"');
> +       }
>         err = read_from_pipe(command_echo, (void **) &command_out, NULL);
>         if (err)
>                 goto errout;
>
> +       for (char *p = command_out; *p; p++) {
> +               SWAP_CHAR('\001', '<');
> +               SWAP_CHAR('\002', '>');
> +               SWAP_CHAR('\003', '"');
> +               SWAP_CHAR('\004', '\'');
> +               SWAP_CHAR('\005', '|');
> +               SWAP_CHAR('\006', '&');
> +       }
> +#undef SWAP_CHAR
>         pr_debug("llvm compiling command : %s\n", command_out);
>
>         err = read_from_pipe(template, &obj_buf, &obj_buf_sz);
> --
> 2.39.0.314.g84b9a713c41-goog
>