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22b96c0dd

Denys Vlasenko
Denys Vlasenko
2026-01-27
SUCCESS Duration: 142s

Subject

ash: unset traps before entering NOEXEC programs after [v]fork

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0 
gcc -Wp,-MD,applets/.usage.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer      -Iinclude -Iinclude -o applets/usage applets/usage.c

Build Log

(log yok)

Commit Diff GitHub →

shell/ash.c +89 -7
shell/ash.c+89 -7
@@ -192,6 +192,7 @@
#define DEBUG_PID 1
#define DEBUG_SIG 1
#define DEBUG_INTONOFF 0
+#define DEBUG_SHOW_MEMUSE 0
#define PROFILE 0
@@ -1117,6 +1118,30 @@ freefunc(struct funcnode *f)
/* ============ Debugging output */
+#if DEBUG_SHOW_MEMUSE
+static void dbg_show_dirtymem(const char *msg)
+{
+ char *p, buf[2*1024];
+ int sz = open_read_close("/proc/self/smaps_rollup", buf, sizeof(buf)-1);
+ if (sz <= 0)
+ return;
+ buf[sz] = '\0';
+ p = buf;
+ for (;;) {
+ char *e = strchrnul(p, '\n');
+ if (strncmp(p, "Private_Dirty:", 14) == 0) {
+ p = skip_whitespace(p + 14);
+ bb_error_msg("%s:%.*s", msg, (int)(e - p), p);
+ break;
+ }
+ if (!*e) break;
+ p = e + 1;
+ }
+}
+#else
+# define dbg_show_dirtymem(msg) ((void)0)
+#endif
+
#if DEBUG
static FILE *tracefile;
@@ -3773,6 +3798,10 @@ ignoresig(int signo)
/*
* Only one usage site - in setsignal()
* This function is called onsig() in dash
+ *
+ * The handler is called only for SIGINT, SIGCHLD, signals with not-"" traps
+ * (grep for S_CATCH handling to see that).
+ * All other signals are either SIG_DFL or SIG_IGN.
*/
static void
signal_handler(int signo)
@@ -3789,9 +3818,10 @@ signal_handler(int signo)
return;
}
#if ENABLE_FEATURE_EDITING
+//TODO: don't do it if it's SIGCHLD?
bb_got_signal = signo; /* for read_line_input / read builtin: "we got a signal" */
#endif
- gotsig[signo - 1] = 1;
+ gotsig[signo - 1] = 1; /* "run a trap for this later" */
pending_sig = signo;
if (signo == SIGINT && !trap[SIGINT]) {
@@ -3819,13 +3849,13 @@ setsignal(int signo)
t = trap[signo];
new_act = S_DFL;
- if (t != NULL) { /* trap for this sig is set */
+ if (t != NULL) {
+ /* Trap for this sig is set */
new_act = S_CATCH;
if (t[0] == '\0') /* trap is "": ignore this sig */
new_act = S_IGN;
- }
-
- if (rootshell && new_act == S_DFL && !lvforked) {
+ } else
+ if (rootshell && /*TRUE: new_act == S_DFL &&*/ !lvforked) {
switch (signo) {
case SIGINT:
if (iflag || minusc || sflag == 0)
@@ -3840,7 +3870,10 @@ setsignal(int signo)
* "In all cases, bash ignores SIGQUIT. Non-builtin
* commands run by bash have signal handlers
* set to the values inherited by the shell
- * from its parent". */
+ * from its parent".
+ * This is not POSIX, but it avoids additional
+ * core files from shells when users press ^\
+ */
new_act = S_IGN;
break;
case SIGTERM:
@@ -5395,7 +5428,7 @@ forkchild(struct job *jp, union node *n, int mode)
}
}
if (oldlvl == 0) {
- if (iflag) { /* why if iflag only? */
+ if (iflag) { /* -i ignores INT/TERM, un-ignore them */
setsignal(SIGINT);
setsignal(SIGTERM);
}
@@ -8449,10 +8482,52 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) const char *cmd, char **argv, c
#if ENABLE_FEATURE_SH_STANDALONE
if (applet_no >= 0) {
if (!vforked && APPLET_IS_NOEXEC(applet_no)) {
+ dbg_show_dirtymem("dirtymem in NOEXEC tryexec");
clearenv();
while (*envp)
putenv(*envp++);
popredir(/*drop:*/ 1);
+//FIXME: exec resets all non-DFL, non-IGN signal handlers to DFL,
+//but we _don't_ exec, such signals will reach ash's handler instead!
+//Maybe add code there to set the handler to DFL, and signal itself?
+// This works for "CMD [| CMD]..." pipes:
+//vforkexec()
+// vfork();
+// forkchild(jp, n, FORK_FG); // this resets TSTP,TTOU,INT,TERM,QUIT to DFL
+// shellexec(argv[0], argv, path, idx)
+// tryexec()
+// we are here
+// And for "exec CMD":
+//execcmd()
+// iflag = 0;
+// mflag = 0;
+// optschanged(); // this resets TSTP,TTOU,INT,TERM to DFL
+// shlvl++;
+// setsignal(SIGQUIT); // this resets QUIT to DFL
+// shellexec()
+// tryexec()
+// we are here
+// But ash -c 'LAST_CMD_DOESNT_FORK' does not work!
+//evalcommand()
+// if (!(flags & EV_EXIT) || may_have_traps)
+// // we don't use this branch
+// //else:
+// shellexec()
+// tryexec()
+// we are here
+//SIGINT works 'by accident' (sets DFL+signals itself)
+//SIGQUIT is IGNORED!
+//Fixed by adding in the evalcommand() before the shown shellexec():
+// shlvl++;
+// setsignal(SIGQUIT);
+// //TODO: setsignal(TSTP,TTOU,INT,TERM) too?
+//
+// With traps set, this:
+// ash -c 'trap "echo HERE!" INT; exec xargs'
+// didn't work: ^C sets a "run trap later" flag and _returns_,
+// which is not expected by the NOFORK'ed xargs!
+// clear_traps() helps with this:
+ clear_traps();
run_noexec_applet_and_exit(applet_no, cmd, argv);
}
/* re-exec ourselves with the new arguments */
@@ -10791,6 +10866,9 @@ evalcommand(union node *cmd, int flags)
jp = vforkexec(cmd, argv, path, cmdentry.u.index);
break;
}
+ /* Testcase: ash -c 'ONE_CMD' will use EV_EXIT for ONE_CMD */
+ shlvl++; /* dash does not need it because it doesn't ignore SIGQUIT */
+ setsignal(SIGQUIT); /* we do (bash compat) */
shellexec(argv[0], argv, path, cmdentry.u.index);
/* NOTREACHED */
} /* default */
@@ -14930,6 +15008,8 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
struct stackmark smark;
int login_sh;
+ dbg_show_dirtymem("dirtymem at main start");
+
/* Initialize global data */
INIT_G_misc();
INIT_G_memstack();
@@ -15030,6 +15110,7 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
// ash -sc 'echo $-'
// continue reading input from stdin after running 'echo'.
// bash does not do this: it prints "hBcs" and exits.
+ dbg_show_dirtymem("dirtymem before -c CMD");
evalstring(minusc, EV_EXIT);
}
@@ -15062,6 +15143,7 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
}
#endif
state4: /* XXX ??? - why isn't this before the "if" statement */
+ dbg_show_dirtymem("dirtymem at cmdloop");
cmdloop(1);
}
#if PROFILE