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Subject[tip: refs/heads/irq/urgent] genirq: Prevent NULL pointer dereference in resend_irqs()
The following commit has been merged into the refs/heads/irq/urgent branch of tip:

Commit-ID: eddf3e9c7c7e4d0707c68d1bb22cc6ec8aef7d4a
Gitweb: https://git.kernel.org/tip/eddf3e9c7c7e4d0707c68d1bb22cc6ec8aef7d4a
Author: Yunfeng Ye <yeyunfeng@huawei.com>
AuthorDate: Wed, 04 Sep 2019 20:46:25 +08:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 05 Sep 2019 21:31:14 +02:00

genirq: Prevent NULL pointer dereference in resend_irqs()

The following crash was observed:

Unable to handle kernel NULL pointer dereference at 0000000000000158
Internal error: Oops: 96000004 [#1] SMP
pc : resend_irqs+0x68/0xb0
lr : resend_irqs+0x64/0xb0
...
Call trace:
resend_irqs+0x68/0xb0
tasklet_action_common.isra.6+0x84/0x138
tasklet_action+0x2c/0x38
__do_softirq+0x120/0x324
run_ksoftirqd+0x44/0x60
smpboot_thread_fn+0x1ac/0x1e8
kthread+0x134/0x138
ret_from_fork+0x10/0x18

The reason for this is that the interrupt resend mechanism happens in soft
interrupt context, which is a asynchronous mechanism versus other
operations on interrupts. free_irq() does not take resend handling into
account. Thus, the irq descriptor might be already freed before the resend
tasklet is executed. resend_irqs() does not check the return value of the
interrupt descriptor lookup and derefences the return value
unconditionally.

1):
__setup_irq
irq_startup
check_irq_resend // activate softirq to handle resend irq
2):
irq_domain_free_irqs
irq_free_descs
free_desc
call_rcu(&desc->rcu, delayed_free_desc)
3):
__do_softirq
tasklet_action
resend_irqs
desc = irq_to_desc(irq)
desc->handle_irq(desc) // desc is NULL --> Ooops

Fix this by adding a NULL pointer check in resend_irqs() before derefencing
the irq descriptor.

Fixes: a4633adcdbc1 ("[PATCH] genirq: add genirq sw IRQ-retrigger")
Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1630ae13-5c8e-901e-de09-e740b6a426a7@huawei.com
---
kernel/irq/resend.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
index 95414ad..98c04ca 100644
--- a/kernel/irq/resend.c
+++ b/kernel/irq/resend.c
@@ -36,6 +36,8 @@ static void resend_irqs(unsigned long arg)
irq = find_first_bit(irqs_resend, nr_irqs);
clear_bit(irq, irqs_resend);
desc = irq_to_desc(irq);
+ if (!desc)
+ continue;
local_irq_disable();
desc->handle_irq(desc);
local_irq_enable();
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