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Fix shared memory crashes in TCP forks #1485

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merged 2 commits into from
Nov 17, 2022
Merged

Fix shared memory crashes in TCP forks #1485

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c689cf2
Add debugging output to verify_shmem_pid()
DL6ER Nov 16, 2022
78597dd
Verify PID of shared memory without remapping global shmSettings object
DL6ER Nov 16, 2022
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43 changes: 14 additions & 29 deletions src/shmem.c
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Original file line number Diff line number Diff line change
Expand Up @@ -135,47 +135,32 @@ static int get_dev_shm_usage(char buffer[64])
// (while we initialized the shared memory objects)
static void verify_shmem_pid(void)
{
const int fd = shm_open(SHARED_SETTINGS_NAME, O_RDWR, S_IRUSR | S_IWUSR);
if(fd == -1)
// Open shared memory settings object
const int settingsfd = shm_open(SHARED_SETTINGS_NAME, O_RDONLY, S_IRUSR | S_IWUSR);
if(settingsfd == -1)
{
logg("FATAL: verify_shmem_pid(): Failed to open shared memory object \"%s\": %s",
SHARED_SETTINGS_NAME, strerror(errno));
exit(EXIT_FAILURE);
}

// Get new pointer
void *shm = mmap(NULL, shm_settings.size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

// Check for `mmap` error
if(shm == MAP_FAILED)
{
logg("FATAL: verify_shmem_pid(): Failed to map shared memory object \"%s\" (%i): %s",
SHARED_SETTINGS_NAME, fd, strerror(errno));
SHARED_SETTINGS_NAME, strerror(errno));
exit(EXIT_FAILURE);
}

// Close file descriptor after call to mmap
close(fd);

// Unmap old memory region
if(munmap(shm_settings.ptr, shm_settings.size) < 0)
ShmSettings shms = { 0 };
if(read(settingsfd, &shms, sizeof(shms)) != sizeof(shms))
{
logg("FATAL: verify_shmem_pid(): Failed to unmap shared memory object \"%s\" (%i): %s",
SHARED_SETTINGS_NAME, fd, strerror(errno));
logg("FATAL: verify_shmem_pid(): Failed to read %zu bytes from shared memory object \"%s\": %s",
sizeof(shms), SHARED_SETTINGS_NAME, strerror(errno));
exit(EXIT_FAILURE);
}

// Update pointer
shmSettings = shm_settings.ptr = shm;
close(settingsfd);

// Compare the SHM's PID to the one we had when creating the SHM objects
if(shmSettings->pid == shmem_pid)
if(shms.pid == shmem_pid)
return;

// If we reach here, we are in serious trouble. Terminating with error
// code is the most sensible thing we can do at this point
logg("FATAL: Shared memory is owned by a different process (PID %d)",
shmSettings->pid);
logg("FATAL: Shared memory is owned by a different process (PID %d)", shms.pid);
check_running_FTL();
logg("Exiting now!");
exit(EXIT_FAILURE);
Expand Down Expand Up @@ -782,6 +767,9 @@ static bool realloc_shm(SharedMemory *sharedMemory, const size_t size1, const si
// TCP requests.
if(resize)
{
// Verify shared memory ownership
verify_shmem_pid();

// Open shared memory object
const int fd = shm_open(sharedMemory->name, O_RDWR, S_IRUSR | S_IWUSR);
if(fd == -1)
Expand Down Expand Up @@ -921,9 +909,6 @@ static size_t get_optimal_object_size(const size_t objsize, const size_t minsize
// Enlarge shared memory to be able to hold at least one new record
void shm_ensure_size(void)
{
// Verify shared memory ownership
verify_shmem_pid();

if(counters->queries >= counters->queries_MAX-1)
{
// Have to reallocate shared memory
Expand Down