[PATCH] Re: Capabilities-related change in 2.5.40

[Chris Wright <chris@wirex.com>]

* Daniel Jacobowitz (dan@debian.org) wrote:
> 
> Yes.  It was pointed out to me that libcap2 snapshots behave correctly.

Ah, thanks for the info.  Hmm, libcap2 still looks like it sets up the
header with pid == 0.  Maybe I'm missing something.

> Not init: swapper.

Yes, although INIT_TASK sets up the task_struct for swapper.

> Try it on 2.4:
> drow@nevyn:~% getpcaps 0
> Capabilities for `0': =
> 
> 2.5.40 gives me a very different answer :)

Heh, you're right.  However, 2.5.20 behaves the same as 2.4.  Looking
back this appears to be caused by 2.5.21 locking cleanups done by rml.
The older code interpreted pid == 0 to mean current, whereas the new
code unconditionally does find_task_by_pid(0).  This patch fixes that,
and then pid == 0 from libcap should work again.

--- 1.5/kernel/capability.c	Sun Sep 15 12:19:29 2002
+++ edited/kernel/capability.c	Wed Oct  2 00:28:32 2002
@@ -33,7 +33,7 @@
      int ret = 0;
      pid_t pid;
      __u32 version;
-     task_t *target;
+     task_t *target = current;
      struct __user_cap_data_struct data;
 
      if (get_user(version, &header->version))
@@ -52,21 +52,20 @@
              return -EINVAL;
 
      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) {
+     	read_lock(&tasklist_lock); 
+     	target = find_task_by_pid(pid);
+     	read_unlock(&tasklist_lock); 
+     	if (!target) {
+          	ret = -ESRCH;
+          	goto out;
+	}
      }
 
-     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:
-     read_unlock(&tasklist_lock); 
      spin_unlock(&task_capability_lock);
 
      if (!ret && copy_to_user(dataptr, &data, sizeof data))

thanks,
-chris
-- 
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