linux-kernel - Re: [PATCH v2 6/9] perf tests: Use scandirat for shell script finding

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Date: Fri, 9 Feb 2024 20:40:54 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, 
	Ravi Bangoria <ravi.bangoria@....com>, James Clark <james.clark@....com>, 
	Kan Liang <kan.liang@...ux.intel.com>, John Garry <john.g.garry@...cle.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v2 6/9] perf tests: Use scandirat for shell script finding

On Wed, Jan 31, 2024 at 4:15 PM Ian Rogers <irogers@...gle.com> wrote:
>
> Avoid filename appending buffers by using openat, faccessat and
> scandirat more widely. Turn the script's path back to a file name
> using readlink from /proc/<pid>/fd/<fd>.
>
> Read the script's description using api/io.h to avoid fdopen
> conversions. Whilst reading perform additional sanity checks on the
> script's contents.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
[SNIP]
> -static const char *shell_test__description(char *description, size_t size,
> -                                           const char *path, const char *name)
> +static char *shell_test__description(int dir_fd, const char *name)
>  {
> -       FILE *fp;
> -       char filename[PATH_MAX];
> -       int ch;
> +       struct io io;
> +       char buf[128], desc[256];
> +       int ch, pos = 0;
>
> -       path__join(filename, sizeof(filename), path, name);
> -       fp = fopen(filename, "r");
> -       if (!fp)
> +       io__init(&io, openat(dir_fd, name, O_RDONLY), buf, sizeof(buf));
> +       if (io.fd < 0)
>                 return NULL;
>
>         /* Skip first line - should be #!/bin/sh Shebang */
> +       if (io__get_char(&io) != '#')
> +               goto err_out;
> +       if (io__get_char(&io) != '!')
> +               goto err_out;
>         do {
> -               ch = fgetc(fp);
> -       } while (ch != EOF && ch != '\n');
> -
> -       description = fgets(description, size, fp);
> -       fclose(fp);
> +               ch = io__get_char(&io);
> +               if (ch < 0)
> +                       goto err_out;
> +       } while (ch != '\n');
>
> -       /* Assume first char on line is omment everything after that desc */
> -       return description ? strim(description + 1) : NULL;
> +       do {
> +               ch = io__get_char(&io);
> +               if (ch < 0)
> +                       goto err_out;
> +       } while (ch == '#' || isspace(ch));
> +       while (ch > 0 && ch != '\n') {
> +               desc[pos++] = ch;
> +               if (pos >= (int)sizeof(desc) - 1)

Maybe (pos == sizeof(desc) - 2) ?  I'm not sure what happens if it has a
description longer than the buffer size.

> +                       break;
> +               ch = io__get_char(&io);
> +       }
> +       while (pos > 0 && isspace(desc[--pos]))
> +               ;
> +       desc[++pos] = '\0';

Wouldn't it overflow the buffer?

Thanks,
Namhyung


> +       close(io.fd);
> +       return strdup(desc);
> +err_out:
> +       close(io.fd);
> +       return NULL;
>  }