[PATCH 2/2] make cap_ptrace enforce PTRACE_TRACME checks

[Chris Wright <chrisw@sous-sol.org>]

PTRACE_TRACEME doesn't have proper capabilities validation when
parent is less privileged than child.  Issue pointed out by
Ram Gupta <ram.gupta5@gmail.com>.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ram Gupta <ram.gupta5@gmail.com>
---
Note: I haven't identified a strong security issue, and it's a small
ABI change that could break apps that rely on existing behaviour (which
allows parent that is less privileged than child to ptrace when child
does PTRACE_TRACEME).

 security/commoncap.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

--- linus-2.6.orig/security/commoncap.c
+++ linus-2.6/security/commoncap.c
@@ -60,8 +60,8 @@ int cap_settime(struct timespec *ts, str
 int cap_ptrace (struct task_struct *parent, struct task_struct *child)
 {
 	/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
-	if (!cap_issubset (child->cap_permitted, current->cap_permitted) &&
-	    !capable(CAP_SYS_PTRACE))
+	if (!cap_issubset(child->cap_permitted, parent->cap_permitted) &&
+	    !__capable(parent, CAP_SYS_PTRACE))
 		return -EPERM;
 	return 0;
 }