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Fix: Replace hardcoded 256-byte shared memory buffer with 4096-byte #516

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Merged
pradeeban merged 2 commits into from
Mar 28, 2026
+67 −11
Merged

Fix: Replace hardcoded 256-byte shared memory buffer with 4096-byte #516

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8d6d989
Fix: Replace hardcoded 256-byte shared memory buffer with 4096-byte S…
GaneshPatil7517 Mar 27, 2026
0af338c
Fix: Add nullptr guard for sharedData_create and shmctl segment size …
GaneshPatil7517 Mar 27, 2026
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44 changes: 38 additions & 6 deletions concore.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,8 @@ class Concore{
string inpath = "./in";
string outpath = "./out";

static constexpr size_t SHM_SIZE = 4096;

int shmId_create = -1;
int shmId_get = -1;

Expand Down Expand Up @@ -259,10 +261,24 @@ class Concore{
*/
void createSharedMemory(key_t key)
{
shmId_create = shmget(key, 256, IPC_CREAT | 0666);
shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);

if (shmId_create == -1) {
std::cerr << "Failed to create shared memory segment." << std::endl;
return;
}

// Verify the segment is large enough (shmget won't resize an existing segment)
struct shmid_ds shm_info;
if (shmctl(shmId_create, IPC_STAT, &shm_info) == 0 && shm_info.shm_segsz < SHM_SIZE) {
std::cerr << "Shared memory segment too small (" << shm_info.shm_segsz
<< " bytes, need " << SHM_SIZE << "). Removing and recreating." << std::endl;
shmctl(shmId_create, IPC_RMID, nullptr);
shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);
if (shmId_create == -1) {
std::cerr << "Failed to recreate shared memory segment." << std::endl;
return;
}
}

// Attach the shared memory segment to the process's address space
Expand All @@ -284,7 +300,7 @@ class Concore{
const int MAX_RETRY = 100;
while (retry < MAX_RETRY) {
// Get the shared memory segment created by Writer
shmId_get = shmget(key, 256, 0666);
shmId_get = shmget(key, SHM_SIZE, 0666);
// Check if shared memory exists
if (shmId_get != -1) {
break; // Break the loop if shared memory exists
Expand Down Expand Up @@ -490,7 +506,7 @@ class Concore{
try {
if (shmId_get != -1) {
if (sharedData_get && sharedData_get[0] != '\0') {
std::string message(sharedData_get, strnlen(sharedData_get, 256));
std::string message(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
ins = message;
}
else
Expand All @@ -515,7 +531,7 @@ class Concore{
this_thread::sleep_for(timespan);
try{
if(shmId_get != -1) {
std::string message(sharedData_get, strnlen(sharedData_get, 256));
std::string message(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
ins = message;
retrycount++;
}
Expand Down Expand Up @@ -658,13 +674,21 @@ class Concore{
try {
std::ostringstream outfile;
if(shmId_create != -1){
if (sharedData_create == nullptr)
throw 506;
val.insert(val.begin(),simtime+delta);
outfile<<'[';
for(int i=0;i<val.size()-1;i++)
outfile<<val[i]<<',';
outfile<<val[val.size()-1]<<']';
std::string result = outfile.str();
std::strncpy(sharedData_create, result.c_str(), 256 - 1);
if (result.size() >= SHM_SIZE) {
std::cerr << "ERROR: write_SM payload (" << result.size()
<< " bytes) exceeds " << SHM_SIZE - 1
<< "-byte shared memory limit. Data truncated!" << std::endl;
}
std::strncpy(sharedData_create, result.c_str(), SHM_SIZE - 1);
sharedData_create[SHM_SIZE - 1] = '\0';
// simtime must not be mutated here (issue #385).
}
else{
Expand All @@ -689,7 +713,15 @@ class Concore{
this_thread::sleep_for(timespan);
try {
if(shmId_create != -1){
std::strncpy(sharedData_create, val.c_str(), 256 - 1);
if (sharedData_create == nullptr)
throw 506;
if (val.size() >= SHM_SIZE) {
std::cerr << "ERROR: write_SM payload (" << val.size()
<< " bytes) exceeds " << SHM_SIZE - 1
<< "-byte shared memory limit. Data truncated!" << std::endl;
}
std::strncpy(sharedData_create, val.c_str(), SHM_SIZE - 1);
sharedData_create[SHM_SIZE - 1] = '\0';
}
else throw 505;
}
Expand Down
34 changes: 29 additions & 5 deletions concoredocker.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@

class Concore {
private:
static constexpr size_t SHM_SIZE = 4096;

int shmId_create = -1;
int shmId_get = -1;
char* sharedData_create = nullptr;
Expand Down Expand Up @@ -233,11 +235,25 @@ class Concore {

#ifdef __linux__
void createSharedMemory(key_t key) {
shmId_create = shmget(key, 256, IPC_CREAT | 0666);
shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);
if (shmId_create == -1) {
std::cerr << "Failed to create shared memory segment.\n";
return;
}

// Verify the segment is large enough (shmget won't resize an existing segment)
struct shmid_ds shm_info;
if (shmctl(shmId_create, IPC_STAT, &shm_info) == 0 && shm_info.shm_segsz < SHM_SIZE) {
std::cerr << "Shared memory segment too small (" << shm_info.shm_segsz
<< " bytes, need " << SHM_SIZE << "). Removing and recreating.\n";
shmctl(shmId_create, IPC_RMID, nullptr);
shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);
if (shmId_create == -1) {
std::cerr << "Failed to recreate shared memory segment.\n";
return;
}
}

sharedData_create = static_cast<char*>(shmat(shmId_create, NULL, 0));
if (sharedData_create == reinterpret_cast<char*>(-1)) {
std::cerr << "Failed to attach shared memory segment.\n";
Expand All @@ -249,7 +265,7 @@ class Concore {
int retry = 0;
const int MAX_RETRY = 100;
while (retry < MAX_RETRY) {
shmId_get = shmget(key, 256, 0666);
shmId_get = shmget(key, SHM_SIZE, 0666);
if (shmId_get != -1)
break;
std::cout << "Shared memory does not exist. Make sure the writer process is running.\n";
Expand Down Expand Up @@ -345,7 +361,7 @@ class Concore {
std::string ins;
try {
if (shmId_get != -1 && sharedData_get && sharedData_get[0] != '\0')
ins = std::string(sharedData_get, strnlen(sharedData_get, 256));
ins = std::string(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
else
throw 505;
} catch (...) {
Expand All @@ -359,7 +375,7 @@ class Concore {
std::this_thread::sleep_for(std::chrono::seconds(delay));
try {
if (shmId_get != -1 && sharedData_get) {
ins = std::string(sharedData_get, strnlen(sharedData_get, 256));
ins = std::string(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
retrycount++;
} else {
retrycount++;
Expand Down Expand Up @@ -419,14 +435,22 @@ class Concore {
try {
if (shmId_create == -1)
throw 505;
if (sharedData_create == nullptr)
throw 506;
val.insert(val.begin(), simtime + delta);
std::ostringstream outfile;
outfile << '[';
for (size_t i = 0; i < val.size() - 1; i++)
outfile << val[i] << ',';
outfile << val[val.size() - 1] << ']';
std::string result = outfile.str();
std::strncpy(sharedData_create, result.c_str(), 256 - 1);
if (result.size() >= SHM_SIZE) {
std::cerr << "ERROR: write_SM payload (" << result.size()
<< " bytes) exceeds " << SHM_SIZE - 1
<< "-byte shared memory limit. Data truncated!" << std::endl;
}
std::strncpy(sharedData_create, result.c_str(), SHM_SIZE - 1);
sharedData_create[SHM_SIZE - 1] = '\0';
} catch (...) {
std::cerr << "skipping +" << outpath << port << "/" << name << "\n";
}
Expand Down
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