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Message-ID: <2d04fa9e-e594-705c-339b-3090cb7d6fbd@huawei.com>
Date: Thu, 12 Oct 2023 17:31:11 +0800
From: ZhaoLong Wang <wangzhaolong1@...wei.com>
To: Zhihao Cheng <chengzhihao1@...wei.com>, <richard@....at>,
<miquel.raynal@...tlin.com>, <vigneshr@...com>
CC: <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
<yi.zhang@...wei.com>, <yangerkun@...wei.com>
Subject: Re: [PATCH RFC] ubi: gluebi: Fix NULL pointer dereference caused by
ftl notifier
>>
>>> 3. P1 P2
>>> gluebi_create -> mtd_device_register -> add_mtd_device:
>>> device_register // dev/mtd1 is visible
>>>
>>> fd = open(/dev/mtd1, O_WRONLY)
>>> gluebi_get_device
>>> gluebi->desc = ubi_open_volume
>>>
>>> ftl_add_mtd
>>> mtd_read
>>> gluebi_read
>>> gluebi->desc is not ERR_PTR/NULL
>>>
>>> close(fd)
>>> gluebi_put_device
>>> ubi_close_volume
>>> kfree(desc)
>>> ubi_read(gluebi->desc) // UAF (×)
>>>
>>
>> Yes, it's also a problem. Perhaps it should be set to NULL after
>> destroying gluebi->desc.
>
> The key point is that 'gluebi->desc' check & usage is not atomic in
> gluebi_read. So following patch still can't handle situation 3.
>
Setting the desc to NULL works because
mutex_lock "mtd_table_mutex" is held on all paths where
ftl_add_mtd() is called.
ubi_gluebi_init
ubi_register_volume_notifier
ubi_enumerate_volumes
ubi_notify_all
gluebi_notify nb->notifier_call()
gluebi_create
mtd_device_register
mtd_device_parse_register
add_mtd_device
mutex_lock(&mtd_table_mutex);
blktrans_notify_add not->add()
ftl_add_mtd tr->add_mtd()
scan_header
mtd_read
mtd_read
mtd_read_oob
gluebi_read mtd->read()
gluebi->desc - NULL
mutex_unlock(&mtd_table_mutex);
ubi_cdev_ioctl
ubi_create_volume
ubi_volume_notify
blocking_notifier_call_chain [kernel/notifier.c]
notifier_call_chain
gluebi_notify nb->notifier_call()
gluebi_create
mtd_device_register
mtd_device_parse_register
add_mtd_device
mutex_lock(&mtd_table_mutex);
blktrans_notify_add not->add()
ftl_add_mtd tr->add_mtd()
scan_header
mtd_read(part->mbd.mtd,
mtd_read_oob
gluebi_read mtd->read()
ubi_read(gluebi->desc
mutex_unlock(&mtd_table_mutex);
load_module ftl
register_mtd_blktrans
mutex_lock(&mtd_table_mutex);
ftl_add_mtd not->add()
scan_header
mtd_read(part->mbd.mtd,
mtd_read_oob
gluebi_read mtd->read()
ubi_read(gluebi->desc
mutex_unlock(&mtd_table_mutex);
This lock is also held during the process of closing the file.
close(fd)
mtdchar_close
put_mtd_device
mutex_lock(&mtd_table_mutex);
__put_mtd_device
gluebi_put_device
ubi_close_volume
kfree(desc)
// desc == NULL
mutex_unlock(&mtd_table_mutex);
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