Re: [BUG] Interactive (d)ash exits on assigning to readonly from 'command eval'

[Denys Vlasenko]

On Sat, Oct 29, 2016 at 8:22 PM, Harald van Dijk  wrote:
> On 28/10/16 15:55, Denys Vlasenko wrote:
>>
>> This will probably be mangled by gmail, but here is the proposed fix:
>
>
> This looks about the right approach, but it causes problems in subshells, a
> double free:
>
> $ ./busybox ash -c 'readonly x; echo $(command eval x=2)'
> ash: eval: line 1: x: is read only
> *** Error in `./busybox': free(): invalid pointer: 0x55a784c1c300 ***
> [...]
>
> That's with busybox checked out from git (commit
> 9db74e49e5b462089c6eec0182d819c0d4708e57), where your patch is applied,
> completely unpatched and completely default config.
>
> I omitted the backtrace output, but it's popfile() getting called, after
> popallfiles() has already been called.

Thanks! Hopefully fixed in git, please try it.
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Re: [BUG] Interactive (d)ash exits on assigning to readonly from 'command eval'

[Denys Vlasenko]

This will probably be mangled by gmail, but here is the proposed fix:

Date: Fri, 28 Oct 2016 15:43:50 +0200
Subject: [PATCH] ash: fix interactive "command eval STRING" exiting on errors.

This bug is also present in current dash

Signed-off-by: Denys Vlasenko 
---
 shell/ash.c | 25 -
 shell/ash_test/ash-vars/readonly1.right |  2 ++
 shell/ash_test/ash-vars/readonly1.tests |  7 +++
 3 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 shell/ash_test/ash-vars/readonly1.right
 create mode 100755 shell/ash_test/ash-vars/readonly1.tests

diff --git a/shell/ash.c b/shell/ash.c
index 1ef02b8..fe11245 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -2180,6 +2180,7 @@ setvareq(char *s, int flags)
 if (flags & VNOSAVE)
 free(s);
 n = vp->var_text;
+exitstatus = 1;
 ash_msg_and_raise_error("%.*s: is read only",
strchrnul(n, '=') - n, n);
 }

@@ -9599,7 +9600,7 @@ evalcommand(union node *cmd, int flags)
 if (evalbltin(cmdentry.u.cmd, argc, argv, flags)) {
 if (exception_type == EXERROR && spclbltin <= 0) {
 FORCE_INT_ON;
-break;
+goto readstatus;
 }
  raise:
 longjmp(exception_handler->loc, 1);
@@ -12280,6 +12281,10 @@ expandstr(const char *ps)
 static int
 evalstring(char *s, int flags)
 {
+struct jmploc *volatile savehandler = exception_handler;
+struct jmploc jmploc;
+int ex;
+
 union node *n;
 struct stackmark smark;
 int status;
@@ -12289,6 +12294,19 @@ evalstring(char *s, int flags)
 setstackmark();

 status = 0;
+/* On exception inside execution loop, we must popfile().
+ * Try interactively:
+ *readonly a=a
+ *command eval "a=b"  # throws "is read only" error
+ * "command BLTIN" is not supposed to abort (even in non-interactive use).
+ * But if we skip popfile(), we hit EOF in eval's string, and exit.
+ */
+savehandler = exception_handler;
+exception_handler = 
+ex = setjmp(jmploc.loc);
+if (ex)
+goto out;
+
 while ((n = parsecmd(0)) != NODE_EOF) {
 int i;

@@ -12299,10 +12317,15 @@ evalstring(char *s, int flags)
 if (evalskip)
 break;
 }
+ out:
 popstackmark();
 popfile();
 stunalloc(s);

+exception_handler = savehandler;
+if (ex)
+longjmp(exception_handler->loc, ex);
+
 return status;
 }

diff --git a/shell/ash_test/ash-vars/readonly1.right
b/shell/ash_test/ash-vars/readonly1.right
new file mode 100644
index 000..2b363e3
--- /dev/null
+++ b/shell/ash_test/ash-vars/readonly1.right
@@ -0,0 +1,2 @@
+One:1
+One:1
diff --git a/shell/ash_test/ash-vars/readonly1.tests
b/shell/ash_test/ash-vars/readonly1.tests
new file mode 100755
index 000..81b461f
--- /dev/null
+++ b/shell/ash_test/ash-vars/readonly1.tests
@@ -0,0 +1,7 @@
+readonly bla=123
+# Bare "eval bla=123" should abort ("eval" is a special builtin):
+(eval bla=123 2>/dev/null; echo BUG)
+echo One:$?
+# "command BLTIN" disables "special-ness", should not abort:
+command eval bla=123 2>/dev/null
+echo One:$?
-- 
2.9.2
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