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Subject[patch 6/9] signal: Fix racy access to __task_cred in kill_pid_info_as_uid()
kill_pid_info_as_uid() accesses __task_cred() without being in a RCU
read side critical section. tasklist_lock is not protecting that when
CONFIG_TREE_PREEMPT_RCU=y.

Convert the whole tasklist_lock section to rcu and use
lock_task_sighand to prevent the exit race.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
---
kernel/signal.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
Index: linux-2.6-tip/kernel/signal.c
===================================================================
--- linux-2.6-tip.orig/kernel/signal.c
+++ linux-2.6-tip/kernel/signal.c
@@ -1175,11 +1175,12 @@ int kill_pid_info_as_uid(int sig, struct
int ret = -EINVAL;
struct task_struct *p;
const struct cred *pcred;
+ unsigned long flags;

if (!valid_signal(sig))
return ret;

- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = pid_task(pid, PIDTYPE_PID);
if (!p) {
ret = -ESRCH;
@@ -1196,14 +1197,16 @@ int kill_pid_info_as_uid(int sig, struct
ret = security_task_kill(p, info, sig, secid);
if (ret)
goto out_unlock;
- if (sig && p->sighand) {
- unsigned long flags;
- spin_lock_irqsave(&p->sighand->siglock, flags);
- ret = __send_signal(sig, info, p, 1, 0);
- spin_unlock_irqrestore(&p->sighand->siglock, flags);
+
+ if (sig) {
+ if (lock_task_sighand(p, &flags)) {
+ ret = __send_signal(sig, info, p, 1, 0);
+ unlock_task_sighand(p, &flags);
+ } else
+ ret = -ESRCH;
}
out_unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return ret;
}
EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);



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