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Yama: higher restrictions should block PTRACE_TRACEME

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The higher ptrace restriction levels should be blocking even
PTRACE_TRACEME requests. The comments in the LSM documentation are
misleading about when the checks happen (the parent does not go through
security_ptrace_access_check() on a PTRACE_TRACEME call).

Signed-off-by: Kees Cook <[email protected]>
Cc: [email protected] # 3.5.x and later
Signed-off-by: James Morris <[email protected]>
This commit is contained in:
Kees Cook 2012-08-09 19:01:26 -07:00 • committed by James Morris
commit 9d8dad742a
3 changed files with 48 additions and 9 deletions
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41
security/yama/yama_lsm.c
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@ -290,10 +290,51 @@ static int yama_ptrace_access_check(struct task_struct *child,
return rc;
}
/**
* yama_ptrace_traceme - validate PTRACE_TRACEME calls
* @parent: task that will become the ptracer of the current task
*
* Returns 0 if following the ptrace is allowed, -ve on error.
*/
static int yama_ptrace_traceme(struct task_struct *parent)
{
int rc;
/* If standard caps disallows it, so does Yama. We should
* only tighten restrictions further.
*/
rc = cap_ptrace_traceme(parent);
if (rc)
return rc;
/* Only disallow PTRACE_TRACEME on more aggressive settings. */
switch (ptrace_scope) {
case YAMA_SCOPE_CAPABILITY:
if (!ns_capable(task_user_ns(parent), CAP_SYS_PTRACE))
rc = -EPERM;
break;
case YAMA_SCOPE_NO_ATTACH:
rc = -EPERM;
break;
}
if (rc) {
char name[sizeof(current->comm)];
printk_ratelimited(KERN_NOTICE
"ptraceme of pid %d was attempted by: %s (pid %d)\n",
current->pid,
get_task_comm(name, parent),
parent->pid);
}
return rc;
}
static struct security_operations yama_ops = {
.name = "yama",
.ptrace_access_check = yama_ptrace_access_check,
.ptrace_traceme = yama_ptrace_traceme,
.task_prctl = yama_task_prctl,
.task_free = yama_task_free,
};