Implementing shared memory without root privilege

Question

I have the following C program

#include <stdio.h>                                                                        
#include <sys/types.h>                                                                    
#include <sys/shm.h>                                                                      
#include <sys/ipc.h>                                                                      

int main()                                                                                
{                                                                                         
  key_t shm_key;                                                                          
  int shm_flag,shm_id,shm_size;                                                           
  void *shm_addr;                                                                         

  shm_key = ftok("/home/meow/Arena",22);                                                  
  perror("SHMKEY");                                                                       

  shm_id = shmget(shm_key,sizeof(int)*20,IPC_CREAT);                                      
  perror("SHMGET");                                                                       

  shm_addr = shmat(shm_id,NULL,0);                                                        
  perror("SHMAT");                                                                     

}

when execute without root privilege I get

meow@darkArts ~/Arena/c $ gcc shm.c && ./a.out 
SHMKEY: Success
SHMGET: Success
SHMAT: Permission denied

And when executed by the root user I get the following message

root@darkArts:/home/meow/Arena/c# gcc shm.c && ./a.out
SHMKEY: Success
SHMGET: Success
SHMAT: Success

Is it possible to bind the shared memory to my address space without the root privileges ?

EDIT:

With shmid = shmget(key, SHMSZ, IPC_CREAT | 0666); and shmid = shmget(key, SHMSZ, IPC_CREAT | 0777); I get

meow@darkArts ~/Arena/c $ gcc shm.c && ./a.out 
SHMKEY: Success
SHMGET: Permission denied
SHMAT: Invalid argument

Did you consider using Posix shared memory? See shm_overview(7) — Basile Starynkevitch
– Basile Starynkevitch, Commented Sep 30, 2014 at 12:22

vvvv · Accepted Answer · 2014-09-30 12:14:13Z

6

You can give permissions to the shared memory segment you create. By default only root is allowed access but you can change this while you create the shared memory segment, for example:

shmid = shmget(key, SHMSZ, IPC_CREAT | 0666); 
//or
shmid = shmget(key, SHMSZ, IPC_CREAT | 0777);

Then you may try and access this shared memory segment as any user.

answered Sep 30, 2014 at 12:14

vvvv

14510 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Implementing shared memory without root privilege

EDIT:

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

EDIT:

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related