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Re: [PATCH v3] Fix writes past the allocated array bounds in execvpe (BZ#20847)
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Mon, 28 Nov 2016 15:56:37 -0200
- Subject: Re: [PATCH v3] Fix writes past the allocated array bounds in execvpe (BZ#20847)
- Authentication-results: sourceware.org; auth=none
- References: <1479908285-7461-1-git-send-email-adhemerval.zanella@linaro.org>
Ping.
On 23/11/2016 11:38, Adhemerval Zanella wrote:
> Commit 6c9e1be87a37bf wrongly fixes BZ#20847 by lefting the else branch
> on maybe_script_execute to still being able to invalid write on stack
> allocated buffer. It happens if execvp{e} is executed with an empty
> arguments list ({ NULL }) and although manual states first argument
> should be the script name itself, by convention, old and current
> implementation allows it.
>
> This patch fixes the issue by just account for arguments and not the
> final 'NULL' (since the 'argv + 1' will indeed ignored the script name).
> The empty argument list is handled in a special case with a minimum
> allocated size. The patch also adds extra tests for such case in
> tst-vfork3.
>
> Tested on x86_64.
>
> [BZ #20847]
> * posix/execvpe.c (maybe_script_execute): Remove write past allocated
> array bounds for else branch.
> (__execvpe): Style fixes.
> * posix/tst-vfork3.c (run_script): New function.
> (create_script): Likewise.
> (do_test): Use run_script internal function.
> (do_prepare): Use create_script internal function.
> ---
> ChangeLog | 12 ++++
> posix/execvpe.c | 19 ++++--
> posix/tst-vfork3.c | 185 +++++++++++++++++++----------------------------------
> 3 files changed, 91 insertions(+), 125 deletions(-)
>
> diff --git a/posix/execvpe.c b/posix/execvpe.c
> index 7cdb06a..a2d0145 100644
> --- a/posix/execvpe.c
> +++ b/posix/execvpe.c
> @@ -38,8 +38,8 @@
> static void
> maybe_script_execute (const char *file, char *const argv[], char *const envp[])
> {
> - ptrdiff_t argc = 0;
> - while (argv[argc++] != NULL)
> + ptrdiff_t argc;
> + for (argc = 0; argv[argc] != NULL; argc++)
> {
> if (argc == INT_MAX - 1)
> {
> @@ -48,13 +48,18 @@ maybe_script_execute (const char *file, char *const argv[], char *const envp[])
> }
> }
>
> - /* Construct an argument list for the shell. It will contain at minimum 3
> - arguments (current shell, script, and an ending NULL. */
> - char *new_argv[argc + 1];
> + /* Construct an argument list for the shell based on original arguments:
> + 1. Empty list (argv = { NULL }, argc = 1 }: new argv will contain 3
> + arguments - default shell, script to execute, and ending NULL.
> + 2. Non empty argument list (argc = { ..., NULL }, argc > 1}: new argv
> + will contain also the default shell and the script to execute. It
> + will also skip the script name in arguments and only copy script
> + arguments. */
> + char *new_argv[argc > 1 ? 2 + argc : 3];
> new_argv[0] = (char *) _PATH_BSHELL;
> new_argv[1] = (char *) file;
> if (argc > 1)
> - memcpy (new_argv + 2, argv + 1, (argc - 1) * sizeof(char *));
> + memcpy (new_argv + 2, argv + 1, argc * sizeof(char *));
> else
> new_argv[2] = NULL;
>
> @@ -96,7 +101,7 @@ __execvpe (const char *file, char *const argv[], char *const envp[])
> size_t path_len = __strnlen (path, PATH_MAX - 1) + 1;
>
> /* NAME_MAX does not include the terminating null character. */
> - if (((file_len-1) > NAME_MAX)
> + if ((file_len - 1 > NAME_MAX)
> || !__libc_alloca_cutoff (path_len + file_len + 1))
> {
> errno = ENAMETOOLONG;
> diff --git a/posix/tst-vfork3.c b/posix/tst-vfork3.c
> index 05edc5a..f5fe5c3 100644
> --- a/posix/tst-vfork3.c
> +++ b/posix/tst-vfork3.c
> @@ -33,84 +33,64 @@ char *tmpdirname;
> #define PREPARE(argc, argv) do_prepare ()
> #include "../test-skeleton.c"
>
> -static int
> -do_test (void)
> +static void
> +run_script (const char *script, char *const argv[])
> {
> - mtrace ();
> -
> - const char *path = getenv ("PATH");
> - if (path == NULL)
> - path = "/bin";
> - char pathbuf[strlen (tmpdirname) + 1 + strlen (path) + 1];
> - strcpy (stpcpy (stpcpy (pathbuf, tmpdirname), ":"), path);
> - if (setenv ("PATH", pathbuf, 1) < 0)
> - {
> - puts ("setenv failed");
> - return 1;
> - }
> -
> - size_t i;
> - char *argv[3] = { (char *) "script1.sh", (char *) "1", NULL };
> - for (i = 0; i < 5; i++)
> + for (size_t i = 0; i < 5; i++)
> {
> pid_t pid = vfork ();
> if (pid < 0)
> - {
> - printf ("vfork failed: %m\n");
> - return 1;
> - }
> + FAIL_EXIT1 ("vfork failed: %m");
> else if (pid == 0)
> {
> - execvp ("script1.sh", argv);
> + execvp (script, argv);
> _exit (errno);
> }
> +
> int status;
> if (TEMP_FAILURE_RETRY (waitpid (pid, &status, 0)) != pid)
> - {
> - puts ("waitpid failed");
> - return 1;
> - }
> + FAIL_EXIT1 ("waitpid failed");
> else if (status != 0)
> {
> if (WIFEXITED (status))
> - printf ("script1.sh failed with status %d\n",
> - WEXITSTATUS (status));
> + FAIL_EXIT1 ("%s failed with status %d\n", script,
> + WEXITSTATUS (status));
> else
> - printf ("script1.sh kill by signal %d\n",
> - WTERMSIG (status));
> - return 1;
> + FAIL_EXIT1 ("%s killed by signal %d\n", script,
> + WTERMSIG (status));
> }
> }
> +}
>
> - argv[0] = (char *) "script2.sh";
> - argv[1] = (char *) "2";
> - for (i = 0; i < 5; i++)
> +static int
> +do_test (void)
> +{
> + mtrace ();
> +
> + const char *path = getenv ("PATH");
> + if (path == NULL)
> + path = "/bin";
> + char pathbuf[strlen (tmpdirname) + 1 + strlen (path) + 1];
> + strcpy (stpcpy (stpcpy (pathbuf, tmpdirname), ":"), path);
> + if (setenv ("PATH", pathbuf, 1) < 0)
> {
> - pid_t pid = vfork ();
> - if (pid < 0)
> - {
> - printf ("vfork failed: %m\n");
> - return 1;
> - }
> - else if (pid == 0)
> - {
> - execvp ("script2.sh", argv);
> - _exit (errno);
> - }
> - int status;
> - if (TEMP_FAILURE_RETRY (waitpid (pid, &status, 0)) != pid)
> - {
> - puts ("waitpid failed");
> - return 1;
> - }
> - else if (status != 0)
> - {
> - printf ("script2.sh failed with status %d\n", status);
> - return 1;
> - }
> + puts ("setenv failed");
> + return 1;
> }
>
> - for (i = 0; i < 5; i++)
> + char *argv00[] = { NULL };
> + run_script ("script0.sh", argv00);
> + char *argv01[] = { (char*) "script0.sh", NULL };
> + run_script ("script0.sh", argv01);
> +
> + char *argv1[] = { (char *) "script1.sh", (char *) "1", NULL };
> + run_script ("script1.sh", argv1);
> +
> + char *argv2[] = { (char *) "script2.sh", (char *) "2", NULL };
> + run_script ("script2.sh", argv2);
> +
> + /* Same as before but with execlp. */
> + for (size_t i = 0; i < 5; i++)
> {
> pid_t pid = vfork ();
> if (pid < 0)
> @@ -137,87 +117,56 @@ do_test (void)
> }
>
> unsetenv ("PATH");
> - argv[0] = (char *) "echo";
> - argv[1] = (char *) "script 4";
> - for (i = 0; i < 5; i++)
> - {
> - pid_t pid = vfork ();
> - if (pid < 0)
> - {
> - printf ("vfork failed: %m\n");
> - return 1;
> - }
> - else if (pid == 0)
> - {
> - execvp ("echo", argv);
> - _exit (errno);
> - }
> - int status;
> - if (TEMP_FAILURE_RETRY (waitpid (pid, &status, 0)) != pid)
> - {
> - puts ("waitpid failed");
> - return 1;
> - }
> - else if (status != 0)
> - {
> - printf ("echo failed with status %d\n", status);
> - return 1;
> - }
> - }
> + char *argv4[] = { (char *) "echo", (char *) "script 4", NULL };
> + run_script ("echo", argv4);
>
> return 0;
> }
>
> static void
> +create_script (const char *script, const char *contents, size_t size)
> +{
> + int fd = open (script, O_WRONLY | O_CREAT, 0700);
> + if (fd < 0
> + || TEMP_FAILURE_RETRY (write (fd, contents, size)) != size
> + || fchmod (fd, S_IRUSR | S_IXUSR) < 0)
> + FAIL_EXIT1 ("could not write %s\n", script);
> + close (fd);
> +}
> +
> +static void
> do_prepare (void)
> {
> size_t len = strlen (test_dir) + sizeof ("/tst-vfork3.XXXXXX");
> tmpdirname = malloc (len);
> - char *script1 = malloc (len + sizeof "/script1.sh");
> - char *script2 = malloc (len + sizeof "/script2.sh");
> - if (tmpdirname == NULL || script1 == NULL || script2 == NULL)
> - {
> - puts ("out of memory");
> - exit (1);
> - }
> + if (tmpdirname == NULL)
> + FAIL_EXIT1 ("out of memory");
> strcpy (stpcpy (tmpdirname, test_dir), "/tst-vfork3.XXXXXX");
>
> tmpdirname = mkdtemp (tmpdirname);
> if (tmpdirname == NULL)
> - {
> - puts ("could not create temporary directory");
> - exit (1);
> - }
> + FAIL_EXIT1 ("could not create temporary directory");
> +
> + char script0[len + sizeof "/script0.sh"];
> + char script1[len + sizeof "/script1.sh"];
> + char script2[len + sizeof "/script2.sh"];
>
> + strcpy (stpcpy (script0, tmpdirname), "/script0.sh");
> strcpy (stpcpy (script1, tmpdirname), "/script1.sh");
> strcpy (stpcpy (script2, tmpdirname), "/script2.sh");
>
> - /* Need to make sure tmpdirname is at the end of the linked list. */
> + add_temp_file (script0);
> add_temp_file (script1);
> - add_temp_file (tmpdirname);
> add_temp_file (script2);
> + /* Need to make sure tmpdirname is at the end of the linked list. */
> + add_temp_file (tmpdirname);
> +
> + const char content0[] = "#!/bin/sh\necho empty\n";
> + create_script (script0, content0, sizeof content0);
>
> const char content1[] = "#!/bin/sh\necho script $1\n";
> - int fd = open (script1, O_WRONLY | O_CREAT, 0700);
> - if (fd < 0
> - || TEMP_FAILURE_RETRY (write (fd, content1, sizeof content1))
> - != sizeof content1
> - || fchmod (fd, S_IRUSR | S_IXUSR) < 0)
> - {
> - printf ("Could not write %s\n", script1);
> - exit (1);
> - }
> - close (fd);
> + create_script (script1, content1, sizeof content1);
>
> const char content2[] = "echo script $1\n";
> - fd = open (script2, O_WRONLY | O_CREAT, 0700);
> - if (fd < 0
> - || TEMP_FAILURE_RETRY (write (fd, content2, sizeof content2))
> - != sizeof content2
> - || fchmod (fd, S_IRUSR | S_IXUSR) < 0)
> - {
> - printf ("Could not write %s\n", script2);
> - exit (1);
> - }
> - close (fd);
> + create_script (script2, content2, sizeof content2);
> }
>