| Message ID | YSy7lOd+qB7LXq1n@zn.tnic |
|---|---|
| State | New |
| Headers | show |
| Series | kthread: Fix PF_KTHREAD vs to_kthread() race | expand |
On Mon, Aug 30, 2021 at 1:06 PM Borislav Petkov <bp@alien8.de> wrote: > > Hi stable folks, > > please queue for 5.10-stable. > > See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. > > --- > Commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 upstream. ... Aha. Seconded, and please also consider for 5.4. This looks lke it could fix the WARNING I reported, seen with 5.4.135, which Igor also saw on 5.10. best regards Patrick
On Mon, Aug 30, 2021 at 01:05:56PM +0200, Borislav Petkov wrote: > Hi stable folks, > > please queue for 5.10-stable. > > See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. Now queued up, thanks. greg k-h
On Wed, Sep 1, 2021 at 11:44 AM Greg KH <greg@kroah.com> wrote: > > On Mon, Aug 30, 2021 at 01:05:56PM +0200, Borislav Petkov wrote: > > > > please queue for 5.10-stable. > > > > See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. > > Now queued up, thanks. I just booted a further of my prod servers with that applied to 5.10.61, patch needed a little mangling, attached below. Once more (as with the 5.4 one), will report about stability in a few days, initially looks fine. best regards Patrick Tested-By: Patrick Schaaf <bof@bof.de> diff -purN linux-5.10.61-orig/kernel/kthread.c linux-5.10.61-p/kernel/kthread.c --- linux-5.10.61-orig/kernel/kthread.c 2021-08-26 14:51:21.000000000 +0200 +++ linux-5.10.61-p/kernel/kthread.c 2021-09-01 09:52:31.056738951 +0200 @@ -84,6 +84,25 @@ 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; @@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_shou */ void *kthread_func(struct task_struct *task) { - if (task->flags & PF_KTHREAD) - return to_kthread(task)->threadfn; + struct kthread *kthread = __to_kthread(task); + if (kthread) + return kthread->threadfn; return NULL; } EXPORT_SYMBOL_GPL(kthread_func); @@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data); */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); + if (kthread) + copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); return data; } @@ -514,9 +535,9 @@ 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; diff -purN linux-5.10.61-orig/kernel/sched/fair.c linux-5.10.61-p/kernel/sched/fair.c --- linux-5.10.61-orig/kernel/sched/fair.c 2021-08-26 14:51:21.000000000 +0200 +++ linux-5.10.61-p/kernel/sched/fair.c 2021-09-01 09:48:06.860333848 +0200 @@ -7569,7 +7569,7 @@ 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/kernel/kthread.c b/kernel/kthread.c index 9825cf89c614..508fe5278285 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -84,6 +84,25 @@ static inline struct kthread *to_kthread(struct task_struct *k) 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; @@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_should_stop); */ void *kthread_func(struct task_struct *task) { - if (task->flags & PF_KTHREAD) - return to_kthread(task)->threadfn; + struct kthread *kthread = __to_kthread(task); + if (kthread) + return kthread->threadfn; return NULL; } EXPORT_SYMBOL_GPL(kthread_func); @@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data); */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); + if (kthread) + copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); return data; } @@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu) 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; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 262b02d75007..bad97d35684d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7569,7 +7569,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) 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)) {
Hi stable folks, please queue for 5.10-stable. See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. --- 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 [ Drop the balance_push() hunk as it is not needed. ] Signed-off-by: Borislav Petkov <bp@suse.de> --- kernel/kthread.c | 33 +++++++++++++++++++++++++++------ kernel/sched/fair.c | 2 +- 2 files changed, 28 insertions(+), 7 deletions(-)