On 12-09-07 04:08 PM, Jonathan Wakely wrote:
On 8 September 2012 00:03, Bob Furber wrote:
Why is the client capable of accessing shared memory when executed by root
and not able to, when executed by a user?
This doesn't sound like it has anything to do with GCC.
After a lot of experimentation, I think the problem lies in shm_open().
The following code generates a /dev/shm/shared with -rw-r--r-- access
privileges, making it inaccessible to others, even though the mode is
set to rw-rw-rw-:
shmfd = shm_open( shm_name, // shared memory block with this "/name"
O_CREAT, // Create if not already there
0666 ); // with these access privileges
Same for:
shmfd = shm_open( shm_name, // shared memory block with this "/name"
O_CREAT, // Create if not already there
| O_RDWR, // allow read and write access
S_IRWXU // 00700 user has rwx privileges
| S_IRWXG // 00070 group has rwx privileges
| S_IRWXO ); // 00007 others has rwx privileges
However, if this is followed by:
fchmod( shmfd,
O_CREAT // Create if not already there
| O_RDWR // allow read and write access
| S_IRWXU // 00700 user (file owner) has rwx privileges
| S_IRWXG // 00070 group (file owner) has rwx privileges
| S_IRWXO ); // 00007 others has rwx privileges
/dev/shm/shared ends up with rw-rw-rw- privileges (since it is not
executable).
smget() was more difficult to troubleshoot because it does not produce a
file descriptor and I could not find the corresponding file to check its
access privileges.
RF
