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gspawn: Don’t use getenv() in async-signal-safe context

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Query the environment before calling `fork()` so that it doesn’t have to
be called in the async-signal-safe context between `fork()` and
`exec()`.

See `man 7 signal-safety`.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #2140
This commit is contained in:
Philip Withnall 2020-06-22 13:59:48 +01:00
parent 84f188ae24
commit 62ce66d4e7
1 changed files with 37 additions and 39 deletions
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76
glib/gspawn.c
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@ -158,10 +158,9 @@ extern char **environ;
static gint safe_close (gint fd); static gint safe_close (gint fd);
static gint g_execute (const gchar *file, static gint g_execute (const gchar *file,
gchar **argv, gchar **argv,
gchar **envp, gchar **envp,
gboolean search_path, const gchar *search_path);
gboolean search_path_from_envp);
static gboolean fork_exec_with_pipes (gboolean intermediate_child, static gboolean fork_exec_with_pipes (gboolean intermediate_child,
const gchar *working_directory, const gchar *working_directory,
@ -1375,8 +1374,7 @@ do_exec (gint child_err_report_fd,
gchar **argv, gchar **argv,
gchar **envp, gchar **envp,
gboolean close_descriptors, gboolean close_descriptors,
gboolean search_path, const gchar *search_path,
gboolean search_path_from_envp,
gboolean stdout_to_null, gboolean stdout_to_null,
gboolean stderr_to_null, gboolean stderr_to_null,
gboolean child_inherits_stdin, gboolean child_inherits_stdin,
@ -1481,7 +1479,7 @@ do_exec (gint child_err_report_fd,
g_execute (argv[0], g_execute (argv[0],
file_and_argv_zero ? argv + 1 : argv, file_and_argv_zero ? argv + 1 : argv,
envp, search_path, search_path_from_envp); envp, search_path);
/* Exec failed */ /* Exec failed */
write_err_and_exit (child_err_report_fd, write_err_and_exit (child_err_report_fd,
@ -1743,6 +1741,7 @@ fork_exec_with_fds (gboolean intermediate_child,
gint child_pid_report_pipe[2] = { -1, -1 }; gint child_pid_report_pipe[2] = { -1, -1 };
guint pipe_flags = cloexec_pipes ? FD_CLOEXEC : 0; guint pipe_flags = cloexec_pipes ? FD_CLOEXEC : 0;
gint status; gint status;
const gchar *chosen_search_path;
#ifdef POSIX_SPAWN_AVAILABLE #ifdef POSIX_SPAWN_AVAILABLE
if (!intermediate_child && working_directory == NULL && !close_descriptors && if (!intermediate_child && working_directory == NULL && !close_descriptors &&
@ -1793,6 +1792,29 @@ fork_exec_with_fds (gboolean intermediate_child,
} }
#endif /* POSIX_SPAWN_AVAILABLE */ #endif /* POSIX_SPAWN_AVAILABLE */
/* Choose a search path. This has to be done before calling fork()
* as getenv() isn’t async-signal-safe (see `man 7 signal-safety`). */
chosen_search_path = NULL;
if (search_path_from_envp)
chosen_search_path = g_environ_getenv (envp, "PATH");
if (search_path && chosen_search_path == NULL)
chosen_search_path = g_getenv ("PATH");
if (chosen_search_path == NULL)
{
/* There is no 'PATH' in the environment. The default
* * search path in libc is the current directory followed by
* * the path 'confstr' returns for '_CS_PATH'.
* */
/* In GLib we put . last, for security, and don't use the
* * unportable confstr(); UNIX98 does not actually specify
* * what to search if PATH is unset. POSIX may, dunno.
* */
chosen_search_path = "/bin:/usr/bin:.";
}
if (!g_unix_open_pipe (child_err_report_pipe, pipe_flags, error)) if (!g_unix_open_pipe (child_err_report_pipe, pipe_flags, error))
return FALSE; return FALSE;
@ -1874,8 +1896,7 @@ fork_exec_with_fds (gboolean intermediate_child,
argv, argv,
envp, envp,
close_descriptors, close_descriptors,
search_path, chosen_search_path,
search_path_from_envp,
stdout_to_null, stdout_to_null,
stderr_to_null, stderr_to_null,
child_inherits_stdin, child_inherits_stdin,
@ -1904,8 +1925,7 @@ fork_exec_with_fds (gboolean intermediate_child,
argv, argv,
envp, envp,
close_descriptors, close_descriptors,
search_path, chosen_search_path,
search_path_from_envp,
stdout_to_null, stdout_to_null,
stderr_to_null, stderr_to_null,
child_inherits_stdin, child_inherits_stdin,
@ -2214,11 +2234,10 @@ my_strchrnul (const gchar *str, gchar c)
/* This function is called between fork() and exec() and hence must be /* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)) until it calls exec(). */ * async-signal-safe (see signal-safety(7)) until it calls exec(). */
static gint static gint
g_execute (const gchar *file, g_execute (const gchar *file,
gchar **argv, gchar **argv,
gchar **envp, gchar **envp,
gboolean search_path, const gchar *search_path)
gboolean search_path_from_envp)
{ {
if (*file == '\0') if (*file == '\0')
{ {
@ -2227,7 +2246,7 @@ g_execute (const gchar *file,
return -1; return -1;
} }
if (!(search_path || search_path_from_envp) || strchr (file, '/') != NULL) if (search_path == NULL || strchr (file, '/') != NULL)
{ {
/* Don't search when it contains a slash. */ /* Don't search when it contains a slash. */
if (envp) if (envp)
@ -2246,28 +2265,7 @@ g_execute (const gchar *file,
gsize len; gsize len;
gsize pathlen; gsize pathlen;
/* FIXME: getenv() is not async-signal-safe */ path = search_path;
path = NULL;
if (search_path_from_envp)
path = g_environ_getenv (envp, "PATH");
if (search_path && path == NULL)
path = g_getenv ("PATH");
if (path == NULL)
{
/* There is no 'PATH' in the environment. The default
* search path in libc is the current directory followed by
* the path 'confstr' returns for '_CS_PATH'.
*/
/* In GLib we put . last, for security, and don't use the
* unportable confstr(); UNIX98 does not actually specify
* what to search if PATH is unset. POSIX may, dunno.
*/
path = "/bin:/usr/bin:.";
}
len = strlen (file) + 1; len = strlen (file) + 1;
pathlen = strlen (path); pathlen = strlen (path);
/* FIXME: malloc() is not async-signal-safe */ /* FIXME: malloc() is not async-signal-safe */