Avoid zero-length calloc (#3280)

Using `calloc` function with a count of zero elements is implementation
defined and it may cause allocation errors on some platforms (ref #3277).
This commit fixes `jv_mem_calloc` callers to avoid undefined behavior.

src/builtin.c

@@ -734,9 +734,12 @@ static jv f_format(jq_state *jq, jv input, jv fmt) {
     input = f_tostring(jq, input);
     const unsigned char* data = (const unsigned char*)jv_string_value(input);
     int len = jv_string_length_bytes(jv_copy(input));
+    if (len == 0) {
+      jv_free(input);
+      return jv_string("");
+    }
     size_t decoded_len = (3 * (size_t)len) / 4; // 3 usable bytes for every 4 bytes of input
     char *result = jv_mem_calloc(decoded_len, sizeof(char));
-    memset(result, 0, decoded_len * sizeof(char));
     uint32_t ri = 0;
     int input_bytes_read=0;
     uint32_t code = 0;

src/compile.c

@@ -1,5 +1,4 @@
 #include <assert.h>
-#include <math.h>
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -7,7 +6,6 @@
 #include "bytecode.h"
 #include "locfile.h"
 #include "jv_alloc.h"
-#include "linker.h"
 
 /*
   The intermediate representation for jq filters is as a sequence of
@@ -1374,7 +1372,7 @@ int block_compile(block b, struct bytecode** out, struct locfile* lf, jv args) {
   bc->globals = jv_mem_alloc(sizeof(struct symbol_table));
   int ncfunc = count_cfunctions(b);
   bc->globals->ncfunctions = 0;
-  bc->globals->cfunctions = jv_mem_calloc(ncfunc, sizeof(struct cfunction));
+  bc->globals->cfunctions = jv_mem_calloc(ncfunc ? ncfunc : 1, sizeof(struct cfunction));
   bc->globals->cfunc_names = jv_array();
   bc->debuginfo = jv_object_set(jv_object(), jv_string("name"), jv_null());
   jv env = jv_invalid();

src/jv_alloc.c

@@ -1,7 +1,8 @@
-#include <stdlib.h>
+#include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
-#include "jv_alloc.h"
+#include "jv.h"
 
 struct nomem_handler {
     jv_nomem_handler_f handler;
@@ -150,6 +151,7 @@ void* jv_mem_alloc_unguarded(size_t sz) {
 }
 
 void* jv_mem_calloc(size_t nemb, size_t sz) {
+  assert(nemb > 0 && sz > 0);
   void* p = calloc(nemb, sz);
   if (!p) {
     memory_exhausted();
@@ -158,6 +160,7 @@ void* jv_mem_calloc(size_t nemb, size_t sz) {
 }
 
 void* jv_mem_calloc_unguarded(size_t nemb, size_t sz) {
+  assert(nemb > 0 && sz > 0);
   return calloc(nemb, sz);
 }
 

src/jv_alloc.h

@@ -2,7 +2,6 @@
 #define JV_ALLOC_H
 
 #include <stddef.h>
-#include "jv.h"
 
 void* jv_mem_alloc(size_t);
 void* jv_mem_alloc_unguarded(size_t);

src/jv_aux.c

@@ -3,6 +3,7 @@
 #include <math.h>
 #include <string.h>
 #include <stdlib.h>
+#include "jv.h"
 #include "jv_alloc.h"
 #include "jv_private.h"
 
@@ -552,6 +553,10 @@ jv jv_keys_unsorted(jv x) {
 jv jv_keys(jv x) {
   if (jv_get_kind(x) == JV_KIND_OBJECT) {
     int nkeys = jv_object_length(jv_copy(x));
+    if (nkeys == 0) {
+      jv_free(x);
+      return jv_array();
+    }
     jv* keys = jv_mem_calloc(nkeys, sizeof(jv));
     int kidx = 0;
     jv_object_foreach(x, key, value) {
@@ -673,6 +678,11 @@ static struct sort_entry* sort_items(jv objects, jv keys) {
   assert(jv_get_kind(keys) == JV_KIND_ARRAY);
   assert(jv_array_length(jv_copy(objects)) == jv_array_length(jv_copy(keys)));
   int n = jv_array_length(jv_copy(objects));
+  if (n == 0) {
+    jv_free(objects);
+    jv_free(keys);
+    return NULL;
+  }
   struct sort_entry* entries = jv_mem_calloc(n, sizeof(struct sort_entry));
   for (int i=0; i<n; i++) {
     entries[i].object = jv_array_get(jv_copy(objects), i);

tests/base64.test

@@ -1,6 +1,10 @@
 # Tests are groups of three lines: program, input, expected output
 # Blank lines and lines starting with # are ignored
 
+@base64
+""
+""
+
 @base64
 "<>&'\"\t"
 "PD4mJyIJ"
@@ -15,6 +19,10 @@
 "foóbar\n"
 "Zm/Ds2Jhcgo="
 
+@base64d
+""
+""
+
 @base64d
 "Zm/Ds2Jhcgo="
 "foóbar\n"