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Message-ID: <CAP-5=fV1dA_hbH=UAZFL8DeuRzvRqW51-gQFSpuEsHpWEDDtWw@mail.gmail.com>
Date: Mon, 12 Feb 2024 08:06:43 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
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 Fri, Feb 9, 2024 at 8:41 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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.
Thanks Namhyung!
sizeof(desc) - 1 == sizeof(char[256]) - 1 == 255 , so at this point
pos can at most be 255 and there is one space after pos for a trailing
'\0'.
> > + break;
> > + ch = io__get_char(&io);
> > + }
> > + while (pos > 0 && isspace(desc[--pos]))
> > + ;
Here pos is moved back to at least one to 254.
> > + desc[++pos] = '\0';
>
> Wouldn't it overflow the buffer?
At this point pos can only have a maximum value of 255 which is within
the bounds of desc.
Thanks,
Ian
> Thanks,
> Namhyung
>
>
> > + close(io.fd);
> > + return strdup(desc);
> > +err_out:
> > + close(io.fd);
> > + return NULL;
> > }
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