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

[wangbiao3]

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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