hush: fix a bug with "stdio rewind on exit". Closes 9186

With FEATURE_SH_STANDALONE=y, run this in a "sh SCRIPT":

sha256sum /dev/null
echo END

sha256sum is a NOEXEC applet. It runs in a forked child. Then child exit()s.
By this time, entire script is read, and buffered in a FILE object
from fopen("SCRIPT"). But fgetc() did not consume entire input.
exit() lseeks back by -9 bytes, from <eof> to 'e' in 'echo'.
(this may be libc-specific).
This change of fd position *is shared with the parent*!

Now parent can read more, and it thinks there is another "echo END".
End result: two "echo END"s are run.

`cmd` and arithmetic also need the fix for this, even without
FEATURE_SH_STANDALONE.

Fix this by _exit()ing instead.

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

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 24253cf27da9c04f60f55962f87cb6af375e4edb..871f78db33e9e5b5eca942926322ce7f1cbf3a17 100644 (file)
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -771,7 +771,9 @@ void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
        }
        if (ENABLE_FEATURE_SUID)
                check_suid(applet_no);
-       exit(applet_main[applet_no](argc, argv));
+       xfunc_error_retval = applet_main[applet_no](argc, argv);
+       /* Note: applet_main() may also not return (die on a xfunc or such) */
+       xfunc_die();
 }
 
 void FAST_FUNC run_applet_and_exit(const char *name, char **argv)

diff --git a/shell/hush.c b/shell/hush.c
index eabe83ac63e33dbcfc87b765a3353fa83704e46c..8bdbd4b8dcd4f1aa0e1779d080cfec4fd4d7739b 100644 (file)
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -1477,19 +1477,50 @@ static sighandler_t install_sighandler(int sig, sighandler_t handler)
        return old_sa.sa_handler;
 }
 
+static void hush_exit(int exitcode) NORETURN;
+static void fflush_and__exit(void) NORETURN;
+static void restore_ttypgrp_and__exit(void) NORETURN;
+
+static void restore_ttypgrp_and__exit(void)
+{
+       /* xfunc has failed! die die die */
+       /* no EXIT traps, this is an escape hatch! */
+       G.exiting = 1;
+       hush_exit(xfunc_error_retval);
+}
+
+/* Needed only on some libc:
+ * It was observed that on exit(), fgetc'ed buffered data
+ * gets "unwound" via lseek(fd, -NUM, SEEK_CUR).
+ * With the net effect that even after fork(), not vfork(),
+ * exit() in NOEXECed applet in "sh SCRIPT":
+ *     noexec_applet_here
+ *     echo END_OF_SCRIPT
+ * lseeks fd in input FILE object from EOF to "e" in "echo END_OF_SCRIPT".
+ * This makes "echo END_OF_SCRIPT" executed twice.
+ * Similar problems can be seen with die_if_script() -> xfunc_die()
+ * and in `cmd` handling.
+ * If set as die_func(), this makes xfunc_die() exit via _exit(), not exit():
+ */
+static void fflush_and__exit(void)
+{
+       fflush_all();
+       _exit(xfunc_error_retval);
+}
+
 #if ENABLE_HUSH_JOB
 
-static void xfunc_has_died(void);
 /* After [v]fork, in child: do not restore tty pgrp on xfunc death */
-# define disable_restore_tty_pgrp_on_exit() (die_func = NULL)
+# define disable_restore_tty_pgrp_on_exit() (die_func = fflush_and__exit)
 /* After [v]fork, in parent: restore tty pgrp on xfunc death */
-# define enable_restore_tty_pgrp_on_exit()  (die_func = xfunc_has_died)
+# define enable_restore_tty_pgrp_on_exit()  (die_func = restore_ttypgrp_and__exit)
 
 /* Restores tty foreground process group, and exits.
  * May be called as signal handler for fatal signal
  * (will resend signal to itself, producing correct exit state)
  * or called directly with -EXITCODE.
- * We also call it if xfunc is exiting. */
+ * We also call it if xfunc is exiting.
+ */
 static void sigexit(int sig) NORETURN;
 static void sigexit(int sig)
 {
@@ -1544,7 +1575,6 @@ static sighandler_t pick_sighandler(unsigned sig)
 }
 
 /* Restores tty foreground process group, and exits. */
-static void hush_exit(int exitcode) NORETURN;
 static void hush_exit(int exitcode)
 {
 #if ENABLE_FEATURE_EDITING_SAVE_ON_EXIT
@@ -1580,23 +1610,14 @@ static void hush_exit(int exitcode)
        }
 #endif
 
-#if ENABLE_HUSH_JOB
        fflush_all();
+#if ENABLE_HUSH_JOB
        sigexit(- (exitcode & 0xff));
 #else
-       exit(exitcode);
+       _exit(exitcode);
 #endif
 }
 
-static void xfunc_has_died(void) NORETURN;
-static void xfunc_has_died(void)
-{
-       /* xfunc has failed! die die die */
-       /* no EXIT traps, this is an escape hatch! */
-       G.exiting = 1;
-       hush_exit(xfunc_error_retval);
-}
-
 
 //TODO: return a mask of ALL handled sigs?
 static int check_and_run_traps(void)
@@ -5913,7 +5934,8 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
                ) {
                        static const char *const argv[] = { NULL, NULL };
                        builtin_trap((char**)argv);
-                       exit(0); /* not _exit() - we need to fflush */
+                       fflush_all(); /* important */
+                       _exit(0);
                }
 # if BB_MMU
                reset_traps_to_defaults();
@@ -6466,7 +6488,8 @@ static void dump_cmd_in_x_mode(char **argv)
  * Never returns.
  * Don't exit() here.  If you don't exec, use _exit instead.
  * The at_exit handlers apparently confuse the calling process,
- * in particular stdin handling.  Not sure why? -- because of vfork! (vda) */
+ * in particular stdin handling. Not sure why? -- because of vfork! (vda)
+ */
 static void pseudo_exec_argv(nommu_save_t *nommu_save,
                char **argv, int assignment_cnt,
                char **argv_expanded) NORETURN;
@@ -7787,6 +7810,7 @@ int hush_main(int argc, char **argv)
        INIT_G();
        if (EXIT_SUCCESS != 0) /* if EXIT_SUCCESS == 0, it is already done */
                G.last_exitcode = EXIT_SUCCESS;
+
 #if ENABLE_HUSH_FAST
        G.count_SIGCHLD++; /* ensure it is != G.handled_SIGCHLD */
 #endif
@@ -7876,7 +7900,7 @@ int hush_main(int argc, char **argv)
        /* Initialize some more globals to non-zero values */
        cmdedit_update_prompt();
 
-       die_func = xfunc_has_died;
+       die_func = restore_ttypgrp_and__exit;
 
        /* Shell is non-interactive at first. We need to call
         * install_special_sighandlers() if we are going to execute "sh <script>",

diff --git a/shell/hush_test/run-all b/shell/hush_test/run-all
index 64a7abc479ae388c559f888da0e52c930a59b12f..837b3f7da100d64b585ffd1a7cd3e048b578b259 100755 (executable)
--- a/shell/hush_test/run-all
+++ b/shell/hush_test/run-all
@@ -64,11 +64,12 @@ do_test()
        echo -n "$1/$x:"
        (
                "$THIS_SH" "./$x" >"$name.xx" 2>&1
+               r=$?
                # filter C library differences
                sed -i \
                        -e "/: invalid option /s:'::g" \
                        "$name.xx"
-               test $? -eq 77 && rm -f "../$1-$x.fail" && exit 77
+               test $r -eq 77 && rm -f "../$1-$x.fail" && exit 77
                diff -u "$name.xx" "$name.right" >"../$1-$x.fail" && rm -f "$name.xx" "../$1-$x.fail"
        )
        case $? in