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Fixed the crash at double-freeing global #25

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merged 1 commit into from
Jun 13, 2023
Merged

Fixed the crash at double-freeing global #25

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24 changes: 15 additions & 9 deletions src/memstack.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,18 +15,25 @@
// the global stack.
memstack* global = NULL;

// Set to 0 if global is not initialized, and 1 if it is.
// Checking for a NULL global is great and all, but the moment we free global
// it breaks.
static int __global_init = 0;

// msinit() is a legacy function used specifically to initialise the global memstack.
// if msinit() is called after the global memstack has already been initialised the
// memstack_chain_ptr* chain will be freed and a new global memstack will be allocated.
void msinit(){

// Check if global has already been initialised or not
if (global == NULL) {
if (__global_init) {
global = msnew();
__global_init = 1;
} else {
// If it is, we free its memory and create a new global memstack
msfree(global);
global = msnew();
__global_init = 1;
}
}

Expand All @@ -51,7 +58,7 @@ memstack* msnew() {
void* msalloc(memstack* storage, int size) {
if(storage == GLOBAL_MEMSTACK) {
// Ensure global is initialised before allocating
if (global != NULL) {
if (__global_init) {
return msalloc(global, size);
} else {
// if not initialised, msalloc() now calls msinit() for the user
Expand Down Expand Up @@ -103,11 +110,12 @@ void free_node(memstack_chain_ptr* node){
// Frees all the nodes stored within the memstack and frees the memstack itself.
void msfree(memstack* storage) {
if (storage == GLOBAL_MEMSTACK) {
// Ensure global is not NULL before freeing
// This is because we dereference global (so we don't want it to be NULL)
if (global != NULL) {
// Ensure global is initialized first
// This is because we dereference global (so we don't want it to be unallocated memory)
if (__global_init) {
free_node(global->first);
free(global);
__global_init = 0;
}
} else {
// If it's not NULL we can free it normally
Expand All @@ -121,9 +129,8 @@ void msclear(memstack* storage) {

// Check if we're clearing global or not
if (storage == GLOBAL_MEMSTACK) {

// Ensure global is not NULL
if (global != NULL) {
if (__global_init) {
msclear(global); // Since global isn't NULL "storage == GLOBAL_MEMSTACK" will be false...
} else {
msinit(); // initialise global if not NULL.
Expand Down Expand Up @@ -232,7 +239,7 @@ void msfprint(memstack* storage, FILE* stream) {

// To handle global memstack
if (storage == GLOBAL_MEMSTACK) {
if (global == NULL)
if (__global_init)
msinit(); // Allocate for the user if needs be

msfprint(global, stream);
Expand Down Expand Up @@ -340,4 +347,3 @@ static void msexit() {
}

#endif