sched/rseq: Fix concurrency ID handling of usermodehelper kthreads

sched_mm_cid_after_execve() does not expect NULL t->mm, but it may happen
if a usermodehelper kthread fails when attempting to execute a binary.

sched_mm_cid_fork() can be issued from a usermodehelper kthread, which
has t->flags PF_KTHREAD set.

Fixes: af7f588d8f73 ("sched: Introduce per-memory-map concurrency ID")
Reported-by: kernel test robot <yujie.liu@intel.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/oe-lkp/202212301353.5c959d72-yujie.liu@intel.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 048ec2417990aae23b82b9a357e6939b179948c0..f99ee69867e3e03487d0d1a92d92b17c19fe2e36 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11343,8 +11343,8 @@ void sched_mm_cid_after_execve(struct task_struct *t)
        struct mm_struct *mm = t->mm;
        unsigned long flags;
 
-       WARN_ON_ONCE((t->flags & PF_KTHREAD) || !t->mm);
-
+       if (!mm)
+               return;
        local_irq_save(flags);
        t->mm_cid = mm_cid_get(mm);
        t->mm_cid_active = 1;
@@ -11354,7 +11354,7 @@ void sched_mm_cid_after_execve(struct task_struct *t)
 
 void sched_mm_cid_fork(struct task_struct *t)
 {
-       WARN_ON_ONCE((t->flags & PF_KTHREAD) || !t->mm || t->mm_cid != -1);
+       WARN_ON_ONCE(!t->mm || t->mm_cid != -1);
        t->mm_cid_active = 1;
 }
 #endif