| Message ID | 20220127205623.1258029-1-tadeusz.struk@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v4] sched/fair: Fix fault in reweight_entity | expand |
On 27/01/2022 21:56, Tadeusz Struk wrote: > 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, -20), wait, and exit. > For each of the new threads the copy_process() gets invoked, which adds > the new task_struct and 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. > To fix the issue the remove the update_load param from the > update_load param() function and call reweight_task() only if the task > flag doesn't have the TASK_NEW flag set. > > 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 v4: > - Removed the update_load param from set_load_weight() and call > reweight_task() based on the TASK_NEW flag > > Changes in v3: > - Removed the new check and changed the update_load condition from > always true to true if p->state != TASK_NEW > > 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 | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 848eaa0efe0e..a0ef4670e695 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1214,10 +1214,12 @@ int tg_nop(struct task_group *tg, void *data) > } > #endif > > -static void set_load_weight(struct task_struct *p, bool update_load) > +static void set_load_weight(struct task_struct *p) > { > int prio = p->static_prio - MAX_RT_PRIO; > struct load_weight *load = &p->se.load; > + bool update_load = !(READ_ONCE(p->__state) & TASK_NEW); nit-pick: reverse fir tree order cat Documentation/process/maintainer-tip.rst | grep -A 10 "Variable declarations" I was able to recreate the initial issue with the reproducer on arm64 Juno-r0 with CONFIG_CGROUP_SCHED=y . Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
On 2/3/22 01:40, Dietmar Eggemann wrote: >> -static void set_load_weight(struct task_struct *p, bool update_load) >> +static void set_load_weight(struct task_struct *p) >> { >> int prio = p->static_prio - MAX_RT_PRIO; >> struct load_weight *load = &p->se.load; >> + bool update_load = !(READ_ONCE(p->__state) & TASK_NEW); > nit-pick: reverse fir tree order > > cat Documentation/process/maintainer-tip.rst | grep -A 10 "Variable > declarations" > > I was able to recreate the initial issue with the reproducer on arm64 > Juno-r0 with CONFIG_CGROUP_SCHED=y . > > Reviewed-by: Dietmar Eggemann<dietmar.eggemann@arm.com> Thanks for reviewing. I will send a v5 soon.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 848eaa0efe0e..a0ef4670e695 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1214,10 +1214,12 @@ int tg_nop(struct task_group *tg, void *data) } #endif -static void set_load_weight(struct task_struct *p, bool update_load) +static void set_load_weight(struct task_struct *p) { int prio = p->static_prio - MAX_RT_PRIO; struct load_weight *load = &p->se.load; + bool update_load = !(READ_ONCE(p->__state) & TASK_NEW); + /* * SCHED_IDLE tasks get minimal weight: @@ -4406,7 +4408,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) p->static_prio = NICE_TO_PRIO(0); p->prio = p->normal_prio = p->static_prio; - set_load_weight(p, false); + set_load_weight(p); /* * We don't need the reset flag anymore after the fork. It has @@ -6921,7 +6923,7 @@ 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); old_prio = p->prio; p->prio = effective_prio(p); @@ -7212,7 +7214,7 @@ static void __setscheduler_params(struct task_struct *p, */ p->rt_priority = attr->sched_priority; p->normal_prio = normal_prio(p); - set_load_weight(p, true); + set_load_weight(p); } /* @@ -9445,7 +9447,7 @@ void __init sched_init(void) #endif } - set_load_weight(&init_task, false); + set_load_weight(&init_task); /* * The boot idle thread does lazy MMU switching as well:
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, -20), wait, and exit. For each of the new threads the copy_process() gets invoked, which adds the new task_struct and 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. To fix the issue the remove the update_load param from the update_load param() function and call reweight_task() only if the task flag doesn't have the TASK_NEW flag set. 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 v4: - Removed the update_load param from set_load_weight() and call reweight_task() based on the TASK_NEW flag Changes in v3: - Removed the new check and changed the update_load condition from always true to true if p->state != TASK_NEW 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 | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)