| Message ID | 20220120200139.118978-1-tadeusz.struk@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] sched/fair: Fix fault in reweight_entity | expand |
On 1/25/22 10:30, Tadeusz Struk wrote: > On 1/25/22 01:14, Vincent Guittot wrote: >> Could we use : >> set_load_weight(p, !(p->__state & TASK_NEW)); >> instead of >> set_load_weight(p, true); >> in set_user_nice and __setscheduler_params. > > Wouldn't that require READ_ONCE() and rmb() after the read? diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 848eaa0efe0e..3d7ede06b971 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6921,7 +6921,7 @@ void set_user_nice(struct task_struct *p, long nice) put_prev_task(rq, p); p->static_prio = NICE_TO_PRIO(nice); - set_load_weight(p, true); + set_load_weight(p, !(READ_ONCE(p->__state) & TASK_NEW)); old_prio = p->prio; p->prio = effective_prio(p); That works for me. I will send a new version soon.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2e4ae00e52d1..c3e74b6d595b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6897,6 +6897,10 @@ void set_user_nice(struct task_struct *p, long nice) if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE) return; + + /* Check if the task's schedule run queue is setup correctly */ + if (!task_rq_ready(p)) + return; /* * We have to be careful, if called from sys_setpriority(), * the task might be in the middle of scheduling on another CPU. diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index de53be905739..464f629bff5a 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1394,6 +1394,12 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp) return grp->my_q; } +/* returns true if cfs run queue is set for the task */ +static inline bool task_rq_ready(struct task_struct *p) +{ + return !!task_cfs_rq(p); +} + #else static inline struct task_struct *task_of(struct sched_entity *se) @@ -1419,6 +1425,11 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp) { return NULL; } + +static inline bool task_rq_ready(struct task_struct *p) +{ + return true; +} #endif extern void update_rq_clock(struct rq *rq);
Syzbot found a GPF in reweight_entity(). This has been bisected to commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group") There is a race between sched_post_fork() and setpriority(PRIO_PGRP) within a thread group that causes a null-ptr-deref in reweight_entity() in CFS. The scenario is that the main process spawns number of new threads, which then call setpriority(PRIO_PGRP, 0, prio), wait, and exit. For each of the new threads the copy_process() gets invoked, which adds the new task_struct to the group, and eventually calls sched_post_fork() for it. In the above scenario there is a possibility that setpriority(PRIO_PGRP) and set_one_prio() will be called for a thread in the group that is just being created by copy_process(), and for which the sched_post_fork() has not been executed yet. This will trigger a null pointer dereference in reweight_entity(), as it will try to access the run queue pointer, which hasn't been set. This results it a crash as shown below: KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7] CPU: 0 PID: 2392 Comm: reduced_repro Not tainted 5.16.0-11201-gb42c5a161ea3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35 04/01/2014 RIP: 0010:reweight_entity+0x15d/0x440 RSP: 0018:ffffc900035dfcf8 EFLAGS: 00010006 Call Trace: <TASK> reweight_task+0xde/0x1c0 set_load_weight+0x21c/0x2b0 set_user_nice.part.0+0x2d1/0x519 set_user_nice.cold+0x8/0xd set_one_prio+0x24f/0x263 __do_sys_setpriority+0x2d3/0x640 __x64_sys_setpriority+0x84/0x8b do_syscall_64+0x35/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae </TASK> ---[ end trace 9dc80a9d378ed00a ]--- Before the mentioned change the cfs_rq pointer for the task has been set in sched_fork(), which is called much earlier in copy_process(), before the new task is added to the thread_group. Now it is done in the sched_post_fork(), which is called after that. Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Segall <bsegall@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Zhang Qiao <zhangqiao22@huawei.com> Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org Link: https://syzkaller.appspot.com/bug?id=9d9c27adc674e3a7932b22b61c79a02da82cbdc1 Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group") Reported-by: syzbot+af7a719bc92395ee41b3@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org> --- Changes in v2: - Added a check in set_user_nice(), and return from there if the task is not fully setup instead of returning from reweight_entity() --- kernel/sched/core.c | 4 ++++ kernel/sched/sched.h | 11 +++++++++++ 2 files changed, 15 insertions(+)