[git commit branch/1_24_stable] hush: fix a bug with "stdio rewind on exit". Closes 9186
Denys Vlasenko
vda.linux at googlemail.com
Fri Aug 19 18:24:49 UTC 2016
commit: https://git.busybox.net/busybox/commit/?id=ca26f1c238c51b3b2f80dd25fd7fcf8774f38ca4
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/1_24_stable
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 at googlemail.com>
---
libbb/appletlib.c | 4 +++-
shell/hush.c | 62 ++++++++++++++++++++++++++++++++++---------------
shell/hush_test/run-all | 3 ++-
3 files changed, 48 insertions(+), 21 deletions(-)
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 24253cf..871f78d 100644
--- 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 eabe83a..8bdbd4b 100644
--- 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 64a7abc..837b3f7 100755
--- 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
More information about the busybox-cvs
mailing list