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Subject: Re: [PATCH] spi: bitbang: Fix NULL pointer dereference in
 spi_unregister_master
To:     YueHaibing <yuehaibing@huawei.com>, broonie@kernel.org,
        axel.lin@ingics.com
Cc:     linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
        albeu@free.fr, lorenzo.bianconi@redhat.com
References: <20190516075656.25880-1-yuehaibing@huawei.com>
From:   Mukesh Ojha <mojha@codeaurora.org>
Message-ID: <e2a15e35-3faf-58be-7b76-5550ddcd49de@codeaurora.org>
Date:   Thu, 16 May 2019 15:13:03 +0530
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On 5/16/2019 1:26 PM, YueHaibing wrote:
> If spi_register_master fails in spi_bitbang_start
> because device_add failure, We should return the
> error code other than 0, otherwise calling
> spi_bitbang_stop may trigger NULL pointer dereference
> like this:
>
> BUG: KASAN: null-ptr-deref in __list_del_entry_valid+0x45/0xd0
> Read of size 8 at addr 0000000000000000 by task syz-executor.0/3661
>
> CPU: 0 PID: 3661 Comm: syz-executor.0 Not tainted 5.1.0+ #28
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
> Call Trace:
>   dump_stack+0xa9/0x10e
>   ? __list_del_entry_valid+0x45/0xd0
>   ? __list_del_entry_valid+0x45/0xd0
>   __kasan_report+0x171/0x18d
>   ? __list_del_entry_valid+0x45/0xd0
>   kasan_report+0xe/0x20
>   __list_del_entry_valid+0x45/0xd0
>   spi_unregister_controller+0x99/0x1b0
>   spi_lm70llp_attach+0x3ae/0x4b0 [spi_lm70llp]
>   ? 0xffffffffc1128000
>   ? klist_next+0x131/0x1e0
>   ? driver_detach+0x40/0x40 [parport]
>   port_check+0x3b/0x50 [parport]
>   bus_for_each_dev+0x115/0x180
>   ? subsys_dev_iter_exit+0x20/0x20
>   __parport_register_driver+0x1f0/0x210 [parport]
>   ? 0xffffffffc1150000
>   do_one_initcall+0xb9/0x3b5
>   ? perf_trace_initcall_level+0x270/0x270
>   ? kasan_unpoison_shadow+0x30/0x40
>   ? kasan_unpoison_shadow+0x30/0x40
>   do_init_module+0xe0/0x330
>   load_module+0x38eb/0x4270
>   ? module_frob_arch_sections+0x20/0x20
>   ? kernel_read_file+0x188/0x3f0
>   ? find_held_lock+0x6d/0xd0
>   ? fput_many+0x1a/0xe0
>   ? __do_sys_finit_module+0x162/0x190
>   __do_sys_finit_module+0x162/0x190
>   ? __ia32_sys_init_module+0x40/0x40
>   ? __mutex_unlock_slowpath+0xb4/0x3f0
>   ? wait_for_completion+0x240/0x240
>   ? vfs_write+0x160/0x2a0
>   ? lockdep_hardirqs_off+0xb5/0x100
>   ? mark_held_locks+0x1a/0x90
>   ? do_syscall_64+0x14/0x2a0
>   do_syscall_64+0x72/0x2a0
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Fixes: 702a4879ec33 ("spi: bitbang: Let spi_bitbang_start() take a reference to master")
> Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>

Cheers,
-Mukesh

> ---
>   drivers/spi/spi-bitbang.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
> index dd9a8c54..be95be4 100644
> --- a/drivers/spi/spi-bitbang.c
> +++ b/drivers/spi/spi-bitbang.c
> @@ -403,7 +403,7 @@ int spi_bitbang_start(struct spi_bitbang *bitbang)
>   	if (ret)
>   		spi_master_put(master);
>   
> -	return 0;
> +	return ret;
>   }
>   EXPORT_SYMBOL_GPL(spi_bitbang_start);
>