ash: catch error in arithmetic expansion in PS1

Setting PS1 to:

   PS1='$((123+))'

causes the shell to enter an infinite error loop:

   sh: arithmetic syntax error

Catch any exception raised by expandarg() in expandstr() and allow
processing to continue.

function                                             old     new   delta
expandstr                                            262     344     +82
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/0 up/down: 82/0)               Total: 82 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 20 insertions, 12 deletions

diff --git a/shell/ash.c b/shell/ash.c
index f3a2c6952..924e17f32 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -13043,6 +13043,9 @@ expandstr(const char *ps, int syntax_type)
         union node n;
         int saveprompt;
         struct parsefile *file_stop = g_parsefile;
+        volatile int saveint;
+        struct jmploc *volatile savehandler = exception_handler;
+        struct jmploc jmploc;
 
         /* XXX Fix (char *) cast. */
         setinputstring((char *)ps);
@@ -13054,18 +13057,13 @@ expandstr(const char *ps, int syntax_type)
          * Try a prompt with syntactically wrong command:
          * PS1='$(date "+%H:%M:%S) > '
          */
-        {
-                volatile int saveint;
-                struct jmploc *volatile savehandler = exception_handler;
-                struct jmploc jmploc;
-                SAVE_INT(saveint);
-                if (setjmp(jmploc.loc) == 0) {
-                        exception_handler = &jmploc;
-                        readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
-                }
-                exception_handler = savehandler;
-                RESTORE_INT(saveint);
+        SAVE_INT(saveint);
+        if (setjmp(jmploc.loc) == 0) {
+                exception_handler = &jmploc;
+                readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
         }
+        exception_handler = savehandler;
+        RESTORE_INT(saveint);
 
         doprompt = saveprompt;
 
@@ -13077,7 +13075,17 @@ expandstr(const char *ps, int syntax_type)
         n.narg.text = wordtext;
         n.narg.backquote = backquotelist;
 
-        expandarg(&n, NULL, EXP_QUOTED);
+        /* expandarg() might fail too:
+         * PS1='$((123+))'
+         */
+        SAVE_INT(saveint);
+        if (setjmp(jmploc.loc) == 0) {
+                exception_handler = &jmploc;
+                expandarg(&n, NULL, EXP_QUOTED);
+        }
+        exception_handler = savehandler;
+        RESTORE_INT(saveint);
+
         return stackblock();
 }