Linux 2.5 and Zsh bug

Linux 2.5 and Zsh bug

[Stephen Hemminger]

When running zsh on a Linux 2.5 kernel, the prompt always has a hash
sign '#' rather than the normal user '$'.  This probably happens because
the shell function privasserted() is returning true for all users.  I
know nothing about Posix capabilities but the zsh code for this looks
suspicious.

Code in question:
------------------------------------------------------------
/* isolate zsh bug */
#include <stdio.h>
#include <sys/capability.h>

int
privasserted(void)
{
   if(!geteuid()) {
       printf("geteuid() is root\n");
       return 1;
   }
   else  {
       cap_t caps = cap_get_proc();
       if(caps) {
           printf("caps = %p\n", caps);
           /* POSIX doesn't define a way to test whether a capability
set *
            * is empty or not.  Typical.  I hope this is
conforming...    */
           cap_flag_value_t val;
           cap_value_t n;

           for(n = 0; !cap_get_flag(caps, n, CAP_EFFECTIVE, &val); n++)
{
               if(val) {
                   printf("capability %#x is %d\n", n, val);
                   cap_free(caps); /* missing in original zsh code
memory leak */
                   return 1;
               }
           }
           printf("last capability %#x\n", n);

           cap_free(caps);
       }
   }
   return 0;
}

int main(int argc, const char **argv) {
   printf("%s privledged\n", privasserted() ?  "Is" : "Not");
}

------------------------------------------------
On 2.4.18
caps = 0x8049844
last capability 0x1d
Not privledged

On 2.5.43
caps = 0x804a00c
capability 0 is 1
Is privledged

Re: Linux 2.5 and Zsh bug

[Chris Wright]

* Stephen Hemminger (shemminger@osdl.org) wrote:
> When running zsh on a Linux 2.5 kernel, the prompt always has a hash
> sign '#' rather than the normal user '$'.  This probably happens because
> the shell function privasserted() is returning true for all users.  I
> know nothing about Posix capabilities but the zsh code for this looks
> suspicious.

See if this patch fixes your problem.  There is a bug in capget(2) which
is called by cap_get_proc(3).  I was holding off on submitting this patch
to Linus until the LSM stuff is resolved.

thanks,
-chris

--- 2.5.43/kernel/capability.c	Sun Sep 15 12:19:29 2002
+++ 2.5.43-capget/kernel/capability.c	Wed Oct 16 00:51:33 2002
@@ -54,15 +54,15 @@
      spin_lock(&task_capability_lock);
      read_lock(&tasklist_lock); 
 
-     target = find_task_by_pid(pid);
-     if (!target) {
-          ret = -ESRCH;
-          goto out;
-     }
+     if (pid && pid != current->pid) {
+	     target = find_task_by_pid(pid);
+	     if (!target) {
+	          ret = -ESRCH;
+	          goto out;
+	     }
+     } else
+	     target = current;
 
-     data.permitted = cap_t(target->cap_permitted);
-     data.inheritable = cap_t(target->cap_inheritable); 
-     data.effective = cap_t(target->cap_effective);
      ret = security_ops->capget(target, &data.effective, &data.inheritable, &data.permitted);
 
 out:
--- 2.5.43/security/dummy.c	Fri Oct 11 14:22:54 2002
+++ 2.5.43-capget/security/dummy.c	Tue Oct 15 00:47:24 2002
@@ -27,6 +27,17 @@
 static int dummy_capget (struct task_struct *target, kernel_cap_t * effective,
 			 kernel_cap_t * inheritable, kernel_cap_t * permitted)
 {
+	*effective = *inheritable = *permitted = 0;
+	if (!issecure(SECURE_NOROOT)) {
+		if (target->euid == 0) {
+			*permitted |= (~0 & ~CAP_FS_MASK);
+			*effective |= (~0 & ~CAP_TO_MASK(CAP_SETPCAP) & ~CAP_FS_MASK);
+		}
+		if (target->fsuid == 0) {
+			*permitted |= CAP_FS_MASK;
+			*effective |= CAP_FS_MASK;
+		}
+	}
 	return 0;
 }
 
-- 
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