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author | Tadeusz Struk <tadeusz.struk@linaro.org> | 2022-02-03 08:18:46 -0800 |
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committer | Peter Zijlstra <peterz@infradead.org> | 2022-02-06 22:37:26 +0100 |
commit | 13765de8148f71fa795e0a6607de37c49ea5915a (patch) | |
tree | fb0cdc627ea53ea86385b3e6d6aa12e624f7186e | |
parent | 26291c54e111ff6ba87a164d85d4a4e134b7315c (diff) | |
download | linux-stable-13765de8148f71fa795e0a6607de37c49ea5915a.tar.gz linux-stable-13765de8148f71fa795e0a6607de37c49ea5915a.tar.bz2 linux-stable-13765de8148f71fa795e0a6607de37c49ea5915a.zip |
sched/fair: Fix fault in reweight_entity
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.
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.
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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20220203161846.1160750-1-tadeusz.struk@linaro.org
-rw-r--r-- | kernel/sched/core.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 848eaa0efe0e..fcf0c180617c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1214,8 +1214,9 @@ 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) { + bool update_load = !(READ_ONCE(p->__state) & TASK_NEW); int prio = p->static_prio - MAX_RT_PRIO; struct load_weight *load = &p->se.load; @@ -4406,7 +4407,7 @@ 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 +6922,7 @@ 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 +7213,7 @@ 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 +9446,7 @@ 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: |