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SubjectRe: [PATCH 1/1] sched: fix user_mask double free
+CC the missing people from get_maintainers.pl

On Monday 21 Nov 2022 at 18:04:20 (+0800), wangbiao3@xiaomi.com wrote:
> From: wangbiao3 <wangbiao3@xiaomi.com>
>
> Clone/Fork a new task,call dup_task_struct->arch_dup_task_struct(tsk,orig)
> which copy the data of parent/sibling task inclding p->user_cpus_ptr,so
> the user_cpus_ptr of newtask is the same with orig task's.When
> dup_task_struct call dup_user_cpus_ptr(tsk, orig, node),it return 0
> dircetly if src->user_cpus_ptris free by other task,in this case ,
> the newtask's address of user_cpus_ptr is not changed. Finally,
> wakup newtask to execute, call task_cpu_possible_mask-->
> do_set_cpus_allowed to set new task's user_cpus_ptr(user_mask) which
> call kfree user_mask at the end. So cause a slub double free panic.
>
> Use pi_lock to protect content of user_cpus_ptr in dup_user_cpus_ptr and
> clear dst->user_cpus_ptr when found src->user_cpus_ptr is null
>
> kernel BUG at mm/slub.c:363!
> Call trace:
> __slab_free+0x230/0x28c
> kfree+0x220/0x2cc
> do_set_cpus_allowed+0x74/0xa4
> select_fallback_rq+0x12c/0x200
> wake_up_new_task+0x26c/0x304
> kernel_clone+0x2c0/0x470
> __arm64_sys_clone+0x5c/0x8c
> invoke_syscall+0x60/0x150
> el0_svc_common.llvm.13030543509303927816+0x98/0x114
> do_el0_svc_compat+0x20/0x30
> el0_svc_compat+0x28/0x90
> el0t_32_sync_handler+0x7c/0xbc
> el0t_32_sync+0x1b8/0x1bc
>
> Signed-off-by: wangbiao3 <wangbiao3@xiaomi.com>
> ---
> kernel/sched/core.c | 31 ++++++++++++++++++++-----------
> 1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index daff72f00385..b013d8b777b4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2584,29 +2584,38 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> __do_set_cpus_allowed(p, new_mask, 0);
> }
>
> +static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
> +{
> + struct cpumask *user_mask = NULL;
> +
> + swap(p->user_cpus_ptr, user_mask);
> +
> + return user_mask;
> +}
> +
> int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
> int node)
> {
> - if (!src->user_cpus_ptr)
> - return 0;

Removing this puts the kmalloc_node() (and kfree()) below on the fast
path for everyone. It wouldn't be surprising if this causes regressions
for some people ...

Can we optimize that?

> + unsigned long flags;
> + struct cpumask *user_mask = NULL;
>
> dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
> if (!dst->user_cpus_ptr)
> return -ENOMEM;
>
> + /* Use pi_lock to protect content of user_cpus_ptr */
> + raw_spin_lock_irqsave(&src->pi_lock, flags);
> + if (!src->user_cpus_ptr) {
> + user_mask = clear_user_cpus_ptr(dst);
> + raw_spin_unlock_irqrestore(&src->pi_lock, flags);
> + kfree(user_mask);
> + return 0;
> + }
> cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
> + raw_spin_unlock_irqrestore(&src->pi_lock, flags);
> return 0;
> }
>
> -static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
> -{
> - struct cpumask *user_mask = NULL;
> -
> - swap(p->user_cpus_ptr, user_mask);
> -
> - return user_mask;
> -}
> -
> void release_user_cpus_ptr(struct task_struct *p)
> {
> kfree(clear_user_cpus_ptr(p));
> --
> 2.38.1
>
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Note that this legalese must be removed from your email before anybody
can apply this patch, please see
Documentation/process/submitting-patches.rst.

Thanks,
Quentin

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