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kthread: Never put_user the set_child_tid address

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Kernel threads abuse set_child_tid.  Historically that has been fine
as set_child_tid was initialized after the kernel thread had been
forked.  Unfortunately storing struct kthread in set_child_tid after
the thread is running makes struct kthread being unusable for storing
result codes of the thread.

When set_child_tid is set to struct kthread during fork that results
in schedule_tail writing the thread id to the beggining of struct
kthread (if put_user does not realize it is a kernel address).

Solve this by skipping the put_user for all kthreads.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lkml.kernel.org/r/YcNsG0Lp94V13whH@archlinux-ax161
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2021-12-22 16:57:50 -06:00
parent dd621ee0cf
commit 00580f03af
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/core.c
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@ -4908,7 +4908,7 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
finish_task_switch(prev);
preempt_enable();
if (current->set_child_tid)
if (!(current->flags & PF_KTHREAD) && current->set_child_tid)
put_user(task_pid_vnr(current), current->set_child_tid);
calculate_sigpending();