[PATCH 1/1] sched: fix user_mask double free

From: wangbiao3
Date: Mon Nov 21 2022 - 05:06:44 EST


From: wangbiao3 <wangbiao3@xxxxxxxxxx>

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@xxxxxxxxxx>
---
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;
+ 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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