CODEWITHSUNDEEP
cpointersqueue
DunkRuZ
DunkRuZ

Reputation: 83

C pointer to pointer and queue

I have method that accepts a pointer to pointer 

typedef struct message_struct_t {
  struct mystruct_t **obj;  //not sure if this correct
  char name[50];
};



int server(mystruct _t **obj) {
   //i am able to push this to a queue
   //but first i store this in my temp struct
   message_struct_t *message = malloc(sizeof(message_struct_t));
   message->obj = obj;
   message->name = "Jaime";
   myqueue_enqueue(message);

   //some mutex and locking mechanism here
   for(int i = 0; i < num_threads; i++)
      pthread_create(&threads[i], NULL, send_message, NULL);
}

I need to get this object and pass it to a method i will be processing in thread pool

   int send_message() {
       //i check and there is an item in my queue, but when i try to assign it to a new struct for 
       //handling i get errors
       struct message_struct *received = malloc(sizeof(message_struct)); //ERROR HERE
       printf("did I get here ? \n", received->name"); //ERROR

       free(received);
   }

The error i am getting is this

  ==20730==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61d0000102b0 at pc 0x55bab7c01cf5 bp 0x7f4d8a2fe980 sp 0x7f4d8a2fe0f8 
    READ of size 2089 at 0x61d0000102b0 thread T1
        #0 0x55bab7c01cf4 in printf_common(void*, char const*, __va_list_tag*) (/project_main+0x5ccf4)

0x61d0000102b0 is located 0 bytes to the right of 2096-byte region [0x61d00000fa80,0x61d0000102b0)
allocated by thread T1 here:
    #0 0x55bab7c6c7b0 in malloc 

in printf_common(void*, char const*, __va_list_tag*)
Shadow bytes around the buggy address:
  0x0c3a7fffa000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    
  0x0c3a7fffa010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    
  0x0c3a7fffa020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    
  0x0c3a7fffa030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    
  0x0c3a7fffa040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    
=>0x0c3a7fffa050: 00 00 00 00 00 00[fa]fa fa fa fa fa fa fa fa fa
  0x0c3a7fffa060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa    
  0x0c3a7fffa070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa    
  0x0c3a7fffa080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa    
  0x0c3a7fffa090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa    
  0x0c3a7fffa0a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa    
Shadow byte legend (one shadow byte represents 8 application bytes): 
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb

Now I am new to C and I may be making some obvious mistake somewhere, I would appreciate some advice as to where I could be assigning wrong (maybe pointers?).

Upvotes: 0

Views: 101

Answers (1)

P0W
P0W

Reputation: 47794

Your send_message should look like following:

void *send_message(void *args) {
    struct message_struct *received  = *((struct message_struct *) args);
    // ....
    free(received );
}

If you cannot change send_message prototype, you will have to wrap it inside a void * func(void *args) somehow, which I believe would be too much of maintaining states for the received message.

Also, you need to make sure you correctly release the acquired resource.

Upvotes: 1

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