yes. the address of "filename" is still in the kernel space. using line 1 and 3 can bypass the address checking in many kernel functions which are originally designed for dealing with user space data. see http://www.linux.it/~rubini/docs/ksys/ksys.html for a detailed description. zhen ----- Original Message ----- From: amith nambiar To: kernelnewbies@nl.linux.org Sent: Monday, September 01, 2003 12:11 AM Subject: get_ds() ?? hi all, i was reading (nearly) Complete Linux loadable kernel modules by - Pragmatic /THC Version 1.0 and found the following. I could understand from the article that whenever system call's are made the arguments must be in user space.Now filename is declared in Kernel space inside my modules as : char filename[]="/home/amisim/logger.txt" extract from the article: ################################################################# ->filename is in our kernel space; a string we just created, for example unsigned long old_fs_value=get_fs(); 1.set_fs(get_ds); /*after this we can access the user space data*/ 2.open(filename, O_CREAT|O_RDWR|O_EXCL, 0640); 3.set_fs(old_fs_value); /*restore fs...*/ ################################################################# Now filename is in our kernel space, but after a call to set_fs(get_ds) the system call works and the system call returns with a fd > 0, how is this working ? i had tried the code without line numbers 1 and 3 (for testing purposes) but it never worked ??. My doubts: 1. "filename" is still in kernel space right ??? 2. what happened in line 1 and 3.? It would be great if someone could throw more light on this.I'am confused :-(. Thanks for your time. regards, Amith. Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
