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From: Kees Cook on 13 Jul 2010 13:40
This cleans up the ancestry check by separating it out into its own
function, which makes the code a bit more readable. Additionally, it
now checks for and uses the thread group leader since otherwise we may
end up missing potential matches on attaches to threads.

Signed-off-by: Kees Cook <kees.cook(a)canonical.com>
---
security/yama/yama_lsm.c | 55 ++++++++++++++++++++++++++++++++-------------
1 files changed, 39 insertions(+), 16 deletions(-)

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 72929d2..3b76386 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -21,6 +21,40 @@ static int protected_sticky_symlinks = 1;
static int protected_nonaccess_hardlinks = 1;

/**
+ * task_is_descendant - walk up a process family tree looking for a match
+ * @parent: the process to compare against while walking up from child
+ * @child: the process to start from while looking upwards for parent
+ *
+ * Returns 1 if child is a descendant of parent, 0 if not.
+ */
+static int task_is_descendant(struct task_struct *parent,
+ struct task_struct *child)
+{
+ int rc = 0;
+ struct task_struct *walker = child;
+
+ if (!parent || !child)
+ return 0;
+
+ rcu_read_lock();
+ read_lock(&tasklist_lock);
+ while (walker->pid > 0) {
+ if (!thread_group_leader(walker))
+ walker = walker->group_leader;
+ if (walker == parent) {
+ rc = 1;
+ break;
+ }
+ walker = walker->real_parent;
+ }
+ read_unlock(&tasklist_lock);
+ rcu_read_unlock();
+
+ return rc;
+}
+
+
+/**
* yama_ptrace_access_check - validate PTRACE_ATTACH calls
* @child: child task pointer
* @mode: ptrace attach mode
@@ -37,22 +71,11 @@ static int yama_ptrace_access_check(struct task_struct *child,
return rc;

/* require ptrace target be a child of ptracer on attach */
- if (mode == PTRACE_MODE_ATTACH && ptrace_scope &&
- !capable(CAP_SYS_PTRACE)) {
- struct task_struct *walker = child;
-
- rcu_read_lock();
- read_lock(&tasklist_lock);
- while (walker->pid > 0) {
- if (walker == current)
- break;
- walker = walker->real_parent;
- }
- if (walker->pid == 0)
- rc = -EPERM;
- read_unlock(&tasklist_lock);
- rcu_read_unlock();
- }
+ if (mode == PTRACE_MODE_ATTACH &&
+ ptrace_scope &&
+ !task_is_descendant(current, child) &&
+ !capable(CAP_SYS_PTRACE))
+ rc = -EPERM;

if (rc) {
char name[sizeof(current->comm)];
--
1.7.1


--
Kees Cook
Ubuntu Security Team
--
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