hush: do not leak script fds into NOEXEC children

We set all opened script fds to CLOEXEC, thus making then go away
after fork+exec.
Unfortunately, CLOFORK does not exist. NOEXEC children will still see those fds open.

For one, "ls" applet is NOEXEC. Therefore running "ls -l /proc/self/fd"
in a script from standalone shell shows this:

lrwx------    1 root     root            64 Aug 20 15:17 0 -> /dev/pts/3
lrwx------    1 root     root            64 Aug 20 15:17 1 -> /dev/pts/3
lrwx------    1 root     root            64 Aug 20 15:17 2 -> /dev/pts/3
lr-x------    1 root     root            64 Aug 20 15:17 3 -> /path/to/top/level/script
lr-x------    1 root     root            64 Aug 20 15:17 4 -> /path/to/sourced/SCRIPT1
...

with as many open fds as there are ". SCRIPTn" nest levels.
Fix it by closing these fds after fork (only for NOEXEC children).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/shell/hush.c b/shell/hush.c
index 9b45b312f3103c95d1a46b53f1d14f08880ff95d..6b0d8503927f729b820c4767a622d59c6e536014 100644 (file)
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -711,6 +711,13 @@ enum {
 };
 
 
+/* Can be extended to handle a FIXME in setup_redirects about not saving script fds */
+struct FILE_list {
+       struct FILE_list *next;
+       FILE *fp;
+};
+
+
 /* "Globals" within this file */
 /* Sorted roughly by size (smaller offsets == smaller code) */
 struct globals {
@@ -801,6 +808,9 @@ struct globals {
        unsigned count_SIGCHLD;
        unsigned handled_SIGCHLD;
        smallint we_have_children;
+#endif
+#if ENABLE_FEATURE_SH_STANDALONE
+       struct FILE_list *FILE_list;
 #endif
        /* Which signals have non-DFL handler (even with no traps set)?
         * Set at the start to:
@@ -1252,6 +1262,54 @@ static void free_strings(char **strings)
 }
 
 
+/* Manipulating the list of open FILEs */
+static FILE *remember_FILE(FILE *fp)
+{
+       if (fp) {
+#if ENABLE_FEATURE_SH_STANDALONE
+               struct FILE_list *n = xmalloc(sizeof(*n));
+               n->fp = fp;
+               n->next = G.FILE_list;
+               G.FILE_list = n;
+#endif
+               close_on_exec_on(fileno(fp));
+       }
+       return fp;
+}
+#if ENABLE_FEATURE_SH_STANDALONE
+static void close_all_FILE_list(void)
+{
+       struct FILE_list *fl = G.FILE_list;
+       while (fl) {
+               /* fclose would also free FILE object.
+                * It is disastrous if we share memory with a vforked parent.
+                * I'm not sure we never come here after vfork.
+                * Therefore just close fd, nothing more.
+                */
+               /*fclose(fl->fp); - unsafe */
+               close(fileno(fl->fp));
+               fl = fl->next;
+       }
+}
+static void fclose_and_forget(FILE *fp)
+{
+       struct FILE_list **pp = &G.FILE_list;
+       while (*pp) {
+               struct FILE_list *cur = *pp;
+               if (cur->fp == fp) {
+                       *pp = cur->next;
+                       free(cur);
+                       break;
+               }
+               pp = &cur->next;
+       }
+       fclose(fp);
+}
+#else
+# define fclose_and_forget(fp) fclose(fp);
+#endif
+
+
 /* Helpers for setting new $n and restoring them back
  */
 typedef struct save_arg_t {
@@ -5968,8 +6026,7 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
        free(to_free);
 # endif
        close(channel[1]);
-       close_on_exec_on(channel[0]);
-       return xfdopen_for_read(channel[0]);
+       return remember_FILE(xfdopen_for_read(channel[0]));
 }
 
 /* Return code is exit status of the process that is run. */
@@ -5998,7 +6055,7 @@ static int process_command_subs(o_string *dest, const char *s)
        }
 
        debug_printf("done reading from `cmd` pipe, closing it\n");
-       fclose(fp);
+       fclose_and_forget(fp);
        /* We need to extract exitcode. Test case
         * "true; echo `sleep 1; false` $?"
         * should print 1 */
@@ -6584,6 +6641,8 @@ static NOINLINE void pseudo_exec_argv(nommu_save_t *nommu_save,
                if (a >= 0) {
 # if BB_MMU /* see above why on NOMMU it is not allowed */
                        if (APPLET_IS_NOEXEC(a)) {
+                               /* Do not leak open fds from opened script files etc */
+                               close_all_FILE_list();
                                debug_printf_exec("running applet '%s'\n", argv[0]);
                                run_applet_no_and_exit(a, argv);
                        }
@@ -8086,10 +8145,10 @@ int hush_main(int argc, char **argv)
                debug_printf("sourcing /etc/profile\n");
                input = fopen_for_read("/etc/profile");
                if (input != NULL) {
-                       close_on_exec_on(fileno(input));
+                       remember_FILE(input);
                        install_special_sighandlers();
                        parse_and_run_file(input);
-                       fclose(input);
+                       fclose_and_forget(input);
                }
                /* bash: after sourcing /etc/profile,
                 * tries to source (in the given order):
@@ -8111,11 +8170,11 @@ int hush_main(int argc, char **argv)
                G.global_argv++;
                debug_printf("running script '%s'\n", G.global_argv[0]);
                input = xfopen_for_read(G.global_argv[0]);
-               close_on_exec_on(fileno(input));
+               remember_FILE(input);
                install_special_sighandlers();
                parse_and_run_file(input);
 #if ENABLE_FEATURE_CLEAN_UP
-               fclose(input);
+               fclose_and_forget(input);
 #endif
                goto final_return;
        }
@@ -8983,7 +9042,7 @@ static int FAST_FUNC builtin_source(char **argv)
                if (arg_path)
                        filename = arg_path;
        }
-       input = fopen_or_warn(filename, "r");
+       input = remember_FILE(fopen_or_warn(filename, "r"));
        free(arg_path);
        if (!input) {
                /* bb_perror_msg("%s", *argv); - done by fopen_or_warn */
@@ -8992,7 +9051,6 @@ static int FAST_FUNC builtin_source(char **argv)
                 */
                return EXIT_FAILURE;
        }
-       close_on_exec_on(fileno(input));
 
 #if ENABLE_HUSH_FUNCTIONS
        sv_flg = G.flag_return_in_progress;
@@ -9003,7 +9061,7 @@ static int FAST_FUNC builtin_source(char **argv)
                save_and_replace_G_args(&sv, argv);
 
        parse_and_run_file(input);
-       fclose(input);
+       fclose_and_forget(input);
 
        if (argv[1])
                restore_G_args(&sv, argv);