(Illustration by Gaich Muramatsu)
Linus, Many Unices have a "setpag" (I called it "newpag") system call through which a process puts itself into a new process authentication group - a new field in process structure. Mostly setpag is called by "login-type" programs, and inherited by fork. This serves authentication which is not necessarily uid based. Filesystems like AFS and Coda like this system for authentication and SMBFS etc could equally use it to their advantage. Will you consider this mini patch which gives us "newpag" and "getpag" system calls, implemented by the students cc'd above? It puts an extra unsigned long in the process structure and defines two mini syscalls and an entry in the /proc/status output. This design was discussed extensively with Ted Ts'o and others, like Bill joined in. There was no protest apart from those who had misunderstood. A fuller motivation is below. I do not know what numbers to assign for sparc, alpha and others. Is lock_kernel() the right way to increment an integer? /**** NOTE ****/ --------> Even if you don't take it note that it patches two little bugs: - .long SYMBOL_NAME(sys_chown) + .long SYMBOL_NAME(sys_lchown) and the syscall numbering was off by one. Below is a fuller motivation. Will you let me know if this is worthy? - Peter - --------------------------------------------- Process Authentication Groups (PAGs) Peter Braam (braam_at_cs.cmu.edu) Tue, 17 Feb 1998 22:24:39 -0500 (EST) Process Authentication Groups ----------------------------- Coda as well as other system services want to implement a stricter form of protection and authentication. Unix authorizes processes based on their uid -- the uid defines a partition of the set of processes. Coda finds this partition into protection groups based on uid too coarse; the sets of processes it wants to authorize should be smaller. For example smbfs and ncpfs need subsets of processes to allow more than one authenticated session to an NT or Novel server, much like Coda. Another example, is that root is not to be trusted lightly but can change its uid easily -- systems based on the Kerberos model don't like this. A further worry arises when telnetd is serving two sessions for the same uid, it is good practice to ask each of these sessions to authenticate. The smaller group of processes for which authentication should give access is called a PAG, a process authentication group. Hopefully defined by the following: - Every process should belong to a pag - Pag's are inherited by fork - at boottime init has a zero pag - when process executes a login related operation (preferrably through a PAM module) this login process would execute a "newpag" system call which places the process in a new PAG. - any process can execute newpag and thereby leave an authentication group of which is was a member - the kernel can return a list of PAG's in use (a la "ps") so that processes holding resources indexed by PAGs can garbage collect resources for PAGS that have gone away. This list will include the pags found under "SAVED_IDS". PAG's are different from process groups and session groups. These change more often and are meant for job control. History ------- The Andrew project used PAGs for AFS authentication. They were "hacked" in the sense that they used 2 fields in the groups array. Root can fairly easily change fields in the group array on some systems -- so this doesn't look so nice. I have no idea what the second field was used for. They called the system call "setpag", but "newpag" seems to better convey semantics. Finally there was/is a special value of pag which was meant to be ignored. I haven't seen the need for this. Implementation -------------- The simplest is to assign a PAGid just like the pid when newpag is executed. This costs one "int" field in the process structure. The PAG can be made increasing and will always be new. Newpag will be a simple system call increasing a global variable maxpag and assigning this to the PAG field in the process structure. We could use /proc/pags to hold a list of pags. One may argue that kernel subsystems may want to hold data related to a PAG and that using a pointer to some kernel data structure - which we can extend as need arises - is more efficient. The worry I have about this is that this pointer may be re-used for a different PAG and that it might be difficult to update all user level processing holding data related to a PAG. How would Coda use PAGS? ------------------------ The following discussion summarizes our ideas about using PAGs for Coda. When a system call reaches the Coda kernel code, Coda queries Venus for access by giving it the PAG as part of the Coda credentials of the process. Venus checks if it has a token for this pag and bases access on this. To get a token a process in the same PAG would use the "clog" (Coda login) program. This negotiates a session key with the auth server (perhaps using Kerberos) and asks the kernel to pass Venus the session key and PAG -- from this moment Venus associates a PAG with a session key. A) session keys for root There are a few interesting issues which relate to root and PAGS. Since PAGS are inherited by fork, it could be very dangerous for a root process to have a session key. Imagine that root has a session key and starts a deamon process. The deamon process would inherit the permissions root has through it's PAG and session key and possibly pass such permissions to any user process requesting service from the daemon. In contrast with this, it is highly desirable that root can start processes which have session keys: however we don't want to give the current PAG those session keys since that could be risky. We propose the following solution: 1) clog will not acquire token for the root user without a further argument. 2) clog can be given a "-e" (for execute) flag. If one were to execute: clog braam -e program Clog would: fork in the child: newpag get a session key exec(program) If roots want a Coda authenticated shell with a key for user moose she would execute: clog moose -e bash B) weaker authentication for special programs Imagine that we are running an NFS server on machine A, and that A is a coda client. We want this nfs server to export /coda to machine B. We assume that the nfs server is well behaved and changes its fsuid to that of the user on behalf of which it is servicing a request. To make this useful we would want a user U on B to telnet to A and create an "unsafe" session key there with "clog --unsafe U". A session key would be given to Venus with a sloppy flag which enables the following: When Venus decides access permissions to serve a request coming from the NFS server, it fails to find a PAG key for the PAG passed by the NFS server. It continues searching for a sloppy key matching the fsuid of the NFS server and grants permissions based on that. - Peter Braam - diff -uNr linux-2.1.100b2.orig/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S --- linux-2.1.100b2.orig/arch/i386/kernel/entry.S Thu Apr 30 18:17:16 1998 +++ linux/arch/i386/kernel/entry.S Tue May 5 17:54:30 1998 @@ -542,9 +542,11 @@ .long SYMBOL_NAME(sys_rt_sigsuspend) .long SYMBOL_NAME(sys_pread) /* 180 */ .long SYMBOL_NAME(sys_pwrite) - .long SYMBOL_NAME(sys_chown) + .long SYMBOL_NAME(sys_lchown) .long SYMBOL_NAME(sys_getcwd) - - .rept NR_syscalls-182 + .long SYMBOL_NAME(sys_newpag) + .long SYMBOL_NAME(sys_getpag) + + .rept NR_syscalls-185 .long SYMBOL_NAME(sys_ni_syscall) .endr diff -uNr linux-2.1.100b2.orig/fs/proc/array.c linux/fs/proc/array.c --- linux-2.1.100b2.orig/fs/proc/array.c Wed Mar 11 18:53:18 1998 +++ linux/fs/proc/array.c Tue May 5 17:50:03 1998 @@ -657,10 +657,12 @@ "PPid:\t%d\n" "Uid:\t%d\t%d\t%d\t%d\n" - "Gid:\t%d\t%d\t%d\t%d\n", + "Gid:\t%d\t%d\t%d\t%d\n" + "Pag:\t%d\n", get_task_state(p), p->pid, p->p_pptr->pid, p->uid, p->euid, p->suid, p->fsuid, - p->gid, p->egid, p->sgid, p->fsgid); + p->gid, p->egid, p->sgid, p->fsgid, + p->pag); return buffer; } @@ -833,7 +835,7 @@ return sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \ %lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %lu %lu %ld %lu %lu %lu %lu %lu \ -%lu %s %s %s %s %lu %lu %lu\n", +%lu %s %s %s %s %lu %lu %lu %lu\n", pid, tsk->comm, state, @@ -870,7 +872,8 @@ sigcatch_str, wchan, tsk->nswap, - tsk->cnswap); + tsk->cnswap, + tsk->pag); } static inline void statm_pte_range(pmd_t * pmd, unsigned long address, unsigned long size, diff -uNr linux-2.1.100b2.orig/include/asm-i386/unistd.h linux/include/asm-i386/unistd.h --- linux-2.1.100b2.orig/include/asm-i386/unistd.h Tue Apr 7 11:05:05 1998 +++ linux/include/asm-i386/unistd.h Tue May 5 17:51:55 1998 @@ -189,6 +189,8 @@ #define __NR_pwrite 181 #define __NR_chown 182 #define __NR_getcwd 183 +#define __NR_newpag 184 +#define __NR_getpag 185 /* user-visible error numbers are in the range -1 - -122: see <asm-i386/errno.h> */ diff -uNr linux-2.1.100b2.orig/include/linux/pag.h linux/include/linux/pag.h --- linux-2.1.100b2.orig/include/linux/pag.h Wed Dec 31 19:00:00 1969 +++ linux/include/linux/pag.h Tue May 5 17:45:48 1998 @@ -0,0 +1,6 @@ +#include <linux/unistd.h> + +_syscall0(unsigned long, newpag); +_syscall0(unsigned long, getpag); + + diff -uNr linux-2.1.100b2.orig/include/linux/sched.h linux/include/linux/sched.h --- linux-2.1.100b2.orig/include/linux/sched.h Thu Apr 30 15:51:34 1998 +++ linux/include/linux/sched.h Tue May 5 17:45:48 1998 @@ -212,6 +212,7 @@ long debugreg[8]; /* Hardware debugging registers */ long counter; long priority; + unsigned long pag; /* Process authentication group */ struct linux_binfmt *binfmt; struct task_struct *next_task, *prev_task; struct task_struct *next_run, *prev_run; @@ -337,6 +338,7 @@ /* state etc */ { 0,0,0,KERNEL_DS,&default_exec_domain, \ /* debugregs */ { 0, }, \ /* counter */ DEF_PRIORITY,DEF_PRIORITY, \ +/* pag */ 0, \ /* binfmt */ NULL, \ /* schedlink */ &init_task,&init_task, &init_task, &init_task, \ /* ec,brk... */ 0,0,0,0,0,0, \ diff -uNr linux-2.1.100b2.orig/kernel/Makefile linux/kernel/Makefile --- linux-2.1.100b2.orig/kernel/Makefile Tue Mar 10 17:43:13 1998 +++ linux/kernel/Makefile Tue May 5 17:45:48 1998 @@ -12,7 +12,7 @@ O_TARGET := kernel.o O_OBJS = sched.o dma.o fork.o exec_domain.o panic.o printk.o sys.o \ - module.o exit.o itimer.o info.o time.o softirq.o resource.o \ + module.o exit.o itimer.o info.o pag.o time.o softirq.o resource.o \ sysctl.o acct.o OX_OBJS += signal.o diff -uNr linux-2.1.100b2.orig/kernel/pag.c linux/kernel/pag.c --- linux-2.1.100b2.orig/kernel/pag.c Wed Dec 31 19:00:00 1969 +++ linux/kernel/pag.c Tue May 5 17:45:48 1998 @@ -0,0 +1,39 @@ +/* + * linux/kernel/pag.c + * + */ + +#include <linux/init.h> +#include <linux/errno.h> +#include <linux/sched.h> +#include <linux/kernel.h> +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/unistd.h> +#include <linux/ptrace.h> +#include <linux/malloc.h> +#include <linux/smp.h> +#include <linux/smp_lock.h> +#include <linux/module.h> + +#include <asm/segment.h> +#include <asm/system.h> +#include <asm/pgtable.h> +#include <asm/mmu_context.h> + +unsigned long int total_pags=1; + +asmlinkage unsigned long sys_newpag(void) +{ + lock_kernel(); + current->pag = total_pags++; + unlock_kernel(); + return 0; +} + +asmlinkage unsigned long sys_getpag(void) +{ + return current->pag; +} + +Received on 1998-05-12 15:48:08