awk: fix printf buffer overflow

function                                             old     new   delta
awk_printf                                           468     546     +78
fmt_num                                              239     247      +8
getvar_s                                             125     111     -14
evaluate                                            3343    3329     -14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/2 up/down: 86/-28)             Total: 58 bytes

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

1 files changed, 55 insertions, 39 deletions

diff --git a/editors/awk.c b/editors/awk.c
index cd135ef64..a440a6234 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -904,25 +904,23 @@ static double my_strtod(char **pp)
 
 /* -------- working with variables (set/get/copy/etc) -------- */
 
-static int fmt_num(char *b, int size, const char *format, double n, int int_as_int)
+static void fmt_num(const char *format, double n)
 {
-        int r = 0;
-        char c;
-        const char *s = format;
-
-        if (int_as_int && n == (long long)n) {
-                r = snprintf(b, size, "%lld", (long long)n);
+        if (n == (long long)n) {
+                snprintf(g_buf, MAXVARFMT, "%lld", (long long)n);
         } else {
+                const char *s = format;
+                char c;
+
                 do { c = *s; } while (c && *++s);
                 if (strchr("diouxX", c)) {
-                        r = snprintf(b, size, format, (int)n);
+                        snprintf(g_buf, MAXVARFMT, format, (int)n);
                 } else if (strchr("eEfFgGaA", c)) {
-                        r = snprintf(b, size, format, n);
+                        snprintf(g_buf, MAXVARFMT, format, n);
                 } else {
                         syntax_error(EMSG_INV_FMT);
                 }
         }
-        return r;
 }
 
 static xhash *iamarray(var *a)
@@ -999,7 +997,7 @@ static const char *getvar_s(var *v)
 {
         /* if v is numeric and has no cached string, convert it to string */
         if ((v->type & (VF_NUMBER | VF_CACHED)) == VF_NUMBER) {
-                fmt_num(g_buf, MAXVARFMT, getvar_s(intvar[CONVFMT]), v->number, TRUE);
+                fmt_num(getvar_s(intvar[CONVFMT]), v->number);
                 v->string = xstrdup(g_buf);
                 v->type |= VF_CACHED;
         }
@@ -2315,12 +2313,9 @@ static int awk_getline(rstream *rsm, var *v)
 #endif
 static char *awk_printf(node *n, int *len)
 {
-        char *b = NULL;
-        char *fmt, *s, *f;
-        const char *s1;
-        int i, j, incr, bsize;
-        char c, c1;
-        var *arg;
+        char *b;
+        char *fmt, *f;
+        int i;
 
         //tmpvar = nvalloc(1);
 #define TMPVAR (&G.awk_printf__tmpvar)
@@ -2333,8 +2328,14 @@ static char *awk_printf(node *n, int *len)
         // to evaluate() potentially recursing into another awk_printf() can't
         // mangle the value.
 
+        b = NULL;
         i = 0;
-        while (*f) {
+        while (*f) { /* "print one format spec" loop */
+                char *s;
+                char c;
+                char sv;
+                var *arg;
+
                 s = f;
                 while (*f && (*f != '%' || *++f == '%'))
                         f++;
@@ -2343,40 +2344,55 @@ static char *awk_printf(node *n, int *len)
                                 syntax_error("%*x formats are not supported");
                         f++;
                 }
-
-                incr = (f - s) + MAXVARFMT;
-                b = qrealloc(b, incr + i, &bsize);
                 c = *f;
-                if (c != '\0')
-                        f++;
-                c1 = *f;
+                if (!c) {
+                        /* Tail of fmt with no percent chars,
+                         * or "....%" (percent seen, but no format specifier char found)
+                         */
+                        goto tail;
+                }
+                sv = *++f;
                 *f = '\0';
                 arg = evaluate(nextarg(&n), TMPVAR);
 
-                j = i;
-                if (c == 'c' || !c) {
-                        i += sprintf(b+i, s, is_numeric(arg) ?
+                /* Result can be arbitrarily long. Example:
+                 *  printf "%99999s", "BOOM"
+                 */
+                if (c == 'c') {
+                        s = xasprintf(s, is_numeric(arg) ?
                                         (char)getvar_i(arg) : *getvar_s(arg));
                 } else if (c == 's') {
-                        s1 = getvar_s(arg);
-                        b = qrealloc(b, incr+i+strlen(s1), &bsize);
-                        i += sprintf(b+i, s, s1);
+                        s = xasprintf(s, getvar_s(arg));
                 } else {
-                        i += fmt_num(b+i, incr, s, getvar_i(arg), FALSE);
+                        double d = getvar_i(arg);
+                        if (strchr("diouxX", c)) {
+//TODO: make it wider here (%x -> %llx etc)?
+                                s = xasprintf(s, (int)d);
+                        } else if (strchr("eEfFgGaA", c)) {
+                                s = xasprintf(s, d);
+                        } else {
+                                syntax_error(EMSG_INV_FMT);
+                        }
                 }
-                *f = c1;
+                *f = sv;
 
-                /* if there was an error while sprintf, return value is negative */
-                if (i < j)
-                        i = j;
+                if (i == 0) {
+                        b = s;
+                        i = strlen(b);
+                        continue;
+                }
+ tail:
+                b = xrealloc(b, i + strlen(s) + 1);
+                i = stpcpy(b + i, s) - b;
+                if (!c) /* tail? */
+                        break;
+                free(s);
         }
 
         free(fmt);
         //nvfree(tmpvar, 1);
 #undef TMPVAR
 
-        b = xrealloc(b, i + 1);
-        b[i] = '\0';
 #if ENABLE_FEATURE_AWK_GNU_EXTENSIONS
         if (len)
                 *len = i;
@@ -2936,8 +2952,8 @@ static var *evaluate(node *op, var *res)
                                         for (;;) {
                                                 var *v = evaluate(nextarg(&op1), TMPVAR0);
                                                 if (v->type & VF_NUMBER) {
-                                                        fmt_num(g_buf, MAXVARFMT, getvar_s(intvar[OFMT]),
-                                                                        getvar_i(v), TRUE);
+                                                        fmt_num(getvar_s(intvar[OFMT]),
+                                                                        getvar_i(v));
                                                         fputs(g_buf, F);
                                                 } else {
                                                         fputs(getvar_s(v), F);