5.4-stable patches

added patches:
	kthread-fix-pf_kthread-vs-to_kthread-race.patch

diff --git a/queue-5.4/kthread-fix-pf_kthread-vs-to_kthread-race.patch b/queue-5.4/kthread-fix-pf_kthread-vs-to_kthread-race.patch
new file mode 100644 (file)
index 0000000..a974a0e
--- /dev/null
+++ b/queue-5.4/kthread-fix-pf_kthread-vs-to_kthread-race.patch
@@ -0,0 +1,146 @@
+From 3a7956e25e1d7b3c148569e78895e1f3178122a9 Mon Sep 17 00:00:00 2001
+From: Peter Zijlstra <peterz@infradead.org>
+Date: Tue, 20 Apr 2021 10:18:17 +0200
+Subject: kthread: Fix PF_KTHREAD vs to_kthread() race
+
+From: Peter Zijlstra <peterz@infradead.org>
+
+commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream.
+
+The kthread_is_per_cpu() construct relies on only being called on
+PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the
+following usage pattern:
+
+       if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
+
+However, as reported by syzcaller, this is broken. The scenario is:
+
+       CPU0                            CPU1 (running p)
+
+       (p->flags & PF_KTHREAD) // true
+
+                                       begin_new_exec()
+                                         me->flags &= ~(PF_KTHREAD|...);
+       kthread_is_per_cpu(p)
+         to_kthread(p)
+           WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT*
+
+Introduce __to_kthread() that omits the WARN and is sure to check both
+values.
+
+Use this to remove the problematic pattern for kthread_is_per_cpu()
+and fix a number of other kthread_*() functions that have similar
+issues but are currently not used in ways that would expose the
+problem.
+
+Notably kthread_func() is only ever called on 'current', while
+kthread_probe_data() is only used for PF_WQ_WORKER, which implies the
+task is from kthread_create*().
+
+Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU")
+Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
+Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
+Link: https://lkml.kernel.org/r/YH6WJc825C4P0FCK@hirez.programming.kicks-ass.net
+Signed-off-by: Patrick Schaaf <bof@bof.de>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ kernel/kthread.c    |   43 +++++++++++++++++++++++++++++--------------
+ kernel/sched/fair.c |    2 +-
+ 2 files changed, 30 insertions(+), 15 deletions(-)
+
+--- a/kernel/kthread.c
++++ b/kernel/kthread.c
+@@ -76,6 +76,25 @@ static inline struct kthread *to_kthread
+       return (__force void *)k->set_child_tid;
+ }
+ 
++/*
++ * Variant of to_kthread() that doesn't assume @p is a kthread.
++ *
++ * Per construction; when:
++ *
++ *   (p->flags & PF_KTHREAD) && p->set_child_tid
++ *
++ * the task is both a kthread and struct kthread is persistent. However
++ * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
++ * begin_new_exec()).
++ */
++static inline struct kthread *__to_kthread(struct task_struct *p)
++{
++      void *kthread = (__force void *)p->set_child_tid;
++      if (kthread && !(p->flags & PF_KTHREAD))
++              kthread = NULL;
++      return kthread;
++}
++
+ void free_kthread_struct(struct task_struct *k)
+ {
+       struct kthread *kthread;
+@@ -176,10 +195,11 @@ void *kthread_data(struct task_struct *t
+  */
+ void *kthread_probe_data(struct task_struct *task)
+ {
+-      struct kthread *kthread = to_kthread(task);
++      struct kthread *kthread = __to_kthread(task);
+       void *data = NULL;
+ 
+-      probe_kernel_read(&data, &kthread->data, sizeof(data));
++      if (kthread)
++              probe_kernel_read(&data, &kthread->data, sizeof(data));
+       return data;
+ }
+ 
+@@ -490,9 +510,9 @@ void kthread_set_per_cpu(struct task_str
+       set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+ }
+ 
+-bool kthread_is_per_cpu(struct task_struct *k)
++bool kthread_is_per_cpu(struct task_struct *p)
+ {
+-      struct kthread *kthread = to_kthread(k);
++      struct kthread *kthread = __to_kthread(p);
+       if (!kthread)
+               return false;
+ 
+@@ -1272,11 +1292,9 @@ EXPORT_SYMBOL(kthread_destroy_worker);
+  */
+ void kthread_associate_blkcg(struct cgroup_subsys_state *css)
+ {
+-      struct kthread *kthread;
++      struct kthread *kthread = __to_kthread(current);
++
+ 
+-      if (!(current->flags & PF_KTHREAD))
+-              return;
+-      kthread = to_kthread(current);
+       if (!kthread)
+               return;
+ 
+@@ -1298,13 +1316,10 @@ EXPORT_SYMBOL(kthread_associate_blkcg);
+  */
+ struct cgroup_subsys_state *kthread_blkcg(void)
+ {
+-      struct kthread *kthread;
++      struct kthread *kthread = __to_kthread(current);
+ 
+-      if (current->flags & PF_KTHREAD) {
+-              kthread = to_kthread(current);
+-              if (kthread)
+-                      return kthread->blkcg_css;
+-      }
++      if (kthread)
++              return kthread->blkcg_css;
+       return NULL;
+ }
+ EXPORT_SYMBOL(kthread_blkcg);
+--- a/kernel/sched/fair.c
++++ b/kernel/sched/fair.c
+@@ -7301,7 +7301,7 @@ int can_migrate_task(struct task_struct
+               return 0;
+ 
+       /* Disregard pcpu kthreads; they are where they need to be. */
+-      if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p))
++      if (kthread_is_per_cpu(p))
+               return 0;
+ 
+       if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {

diff --git a/queue-5.4/series b/queue-5.4/series
index 099470196dba1080cb1f90de51c47571a139f907..c9f3c329a62e30a35596f9792a31b437e691ee42 100644 (file)
--- a/queue-5.4/series
+++ b/queue-5.4/series
@@ -3,3 +3,4 @@ fscrypt-add-fscrypt_symlink_getattr-for-computing-st_size.patch
 ext4-report-correct-st_size-for-encrypted-symlinks.patch
 f2fs-report-correct-st_size-for-encrypted-symlinks.patch
 ubifs-report-correct-st_size-for-encrypted-symlinks.patch
+kthread-fix-pf_kthread-vs-to_kthread-race.patch