From f2cc3eb133baa2e9dc8efd40f417106b2ee520f3 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 8 Feb 2008 04:19:06 -0800 Subject: [PATCH] do_wait: fix security checks Imho, the current usage of security_task_wait() is not logical. Suppose we have the single child p, and security_task_wait(p) return -EANY. In that case waitpid(-1) returns this error. Why? Isn't it better to return ECHLD? We don't really have reapable children. Now suppose that child was stolen by gdb. In that case we find this child on ->ptrace_children and set flag = 1, but we don't check that the child was denied. So, do_wait(..., WNOHANG) returns 0, this doesn't match the behaviour above. Without WNOHANG do_wait() blocks only to return the error later, when the child will be untraced. Inho, really strange. I think eligible_child() should return the error only if the child's pid was requested explicitly, otherwise we should silently ignore the tasks which were nacked by security_task_wait(). Signed-off-by: Oleg Nesterov Cc: Roland McGrath Cc: Chris Wright Cc: Eric Paris Cc: James Morris Cc: Stephen Smalley Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/exit.c | 39 ++++++++++++++++++--------------------- 1 file changed, 18 insertions(+), 21 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 9ee229ea97e4..ee607720ae58 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1142,10 +1142,14 @@ static int eligible_child(pid_t pid, int options, struct task_struct *p) return 0; err = security_task_wait(p); - if (err) - return err; + if (likely(!err)) + return 1; - return 1; + if (pid <= 0) + return 0; + /* This child was explicitly requested, abort */ + read_unlock(&tasklist_lock); + return err; } static int wait_noreap_copyout(struct task_struct *p, pid_t pid, uid_t uid, @@ -1476,7 +1480,6 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, DECLARE_WAITQUEUE(wait, current); struct task_struct *tsk; int flag, retval; - int allowed, denied; add_wait_queue(¤t->signal->wait_chldexit,&wait); repeat: @@ -1484,8 +1487,7 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, * We will set this flag if we see any child that might later * match our criteria, even if we are not able to reap it yet. */ - flag = 0; - allowed = denied = 0; + flag = retval = 0; current->state = TASK_INTERRUPTIBLE; read_lock(&tasklist_lock); tsk = current; @@ -1498,13 +1500,8 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, continue; if (unlikely(ret < 0)) { - denied = ret; - continue; - } - allowed = 1; - - retval = 0; - if (task_is_stopped_or_traced(p)) { + retval = ret; + } else if (task_is_stopped_or_traced(p)) { /* * It's stopped now, so it might later * continue, exit, or stop again. @@ -1544,11 +1541,14 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, } if (!flag) { list_for_each_entry(p, &tsk->ptrace_children, - ptrace_list) { - if (!eligible_child(pid, options, p)) + ptrace_list) { + flag = eligible_child(pid, options, p); + if (!flag) continue; - flag = 1; - break; + if (likely(flag > 0)) + break; + retval = flag; + goto end; } } if (options & __WNOTHREAD) @@ -1556,10 +1556,9 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, tsk = next_thread(tsk); BUG_ON(tsk->signal != current->signal); } while (tsk != current); - read_unlock(&tasklist_lock); + if (flag) { - retval = 0; if (options & WNOHANG) goto end; retval = -ERESTARTSYS; @@ -1569,8 +1568,6 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop, goto repeat; } retval = -ECHILD; - if (unlikely(denied) && !allowed) - retval = denied; end: current->state = TASK_RUNNING; remove_wait_queue(¤t->signal->wait_chldexit,&wait); -- GitLab