awk: do not allow $(-1)

function                                             old     new   delta
EMSG_NEGATIVE_FIELD                                    -      25     +25
evaluate                                            3390    3403     +13
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/0 up/down: 38/0)               Total: 38 bytes

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

2 files changed, 9 insertions, 0 deletions

diff --git a/editors/awk.c b/editors/awk.c
index d54249bfd..bafc9ba1d 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -598,6 +598,7 @@ static const char EMSG_NOT_ARRAY[] ALIGN1 = "Not an array";
 static const char EMSG_POSSIBLE_ERROR[] ALIGN1 = "Possible syntax error";
 static const char EMSG_UNDEF_FUNC[] ALIGN1 = "Call to undefined function";
 static const char EMSG_NO_MATH[] ALIGN1 = "Math support is not compiled in";
+static const char EMSG_NEGATIVE_FIELD[] ALIGN1 = "Access to negative field";
 
 static void zero_out_var(var *vp)
 {
@@ -2949,6 +2950,8 @@ static var *evaluate(node *op, var *res)
 
                 case XC( OC_FIELD ): {
                         int i = (int)getvar_i(R.v);
+                        if (i < 0)
+                                syntax_error(EMSG_NEGATIVE_FIELD);
                         if (i == 0) {
                                 res = intvar[F0];
                         } else {
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index ad0583afb..3933fefc9 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -339,5 +339,11 @@ testing "awk handles invalid for loop" \
     "awk '{ for() }' 2>&1" "awk: cmd. line:1: Unexpected token\n" "" ""
 
 # testing "description" "command" "result" "infile" "stdin"
+testing 'awk negative field access' \
+        'awk 2>&1 -- '\''{ $(-1) }'\' \
+        "awk: cmd. line:1: Access to negative field\n" \
+        '' \
+        'anything'
+
 
 exit $FAILCOUNT