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Subject: Re: [PATCH -next] jffs2: fix use-after-free in
 jffs2_clear_xattr_subsystem
To:     Richard Weinberger <richard@nod.at>
CC:     David Woodhouse <dwmw2@infradead.org>,
        christian brauner <christian.brauner@ubuntu.com>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        yukuai3 <yukuai3@huawei.com>, stable <stable@vger.kernel.org>,
        Hulk Robot <hulkci@huawei.com>,
        Baokun Li <libaokun1@huawei.com>
References: <20211228125430.1880252-1-libaokun1@huawei.com>
 <8a175ec6-1555-8575-1f03-0002efac1740@huawei.com>
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From:   "libaokun (A)" <libaokun1@huawei.com>
Message-ID: <2eb626fe-3ab2-2830-12b7-0de74ddd9258@huawei.com>
Date:   Thu, 17 Mar 2022 09:29:11 +0800
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在 2022/3/17 6:01, Richard Weinberger 写道:
> ----- Ursprüngliche Mail -----
>> Von: "libaokun" <libaokun1@huawei.com>
>> An: "richard" <richard@nod.at>, "David Woodhouse" <dwmw2@infradead.org>, "christian brauner"
>> <christian.brauner@ubuntu.com>, "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel"
>> <linux-kernel@vger.kernel.org>
>> CC: "yukuai3" <yukuai3@huawei.com>, "stable" <stable@vger.kernel.org>, "Hulk Robot" <hulkci@huawei.com>, "libaokun"
>> <libaokun1@huawei.com>
>> Gesendet: Donnerstag, 10. März 2022 09:35:18
>> Betreff: Re: [PATCH -next] jffs2: fix use-after-free in jffs2_clear_xattr_subsystem
>> A gentle ping, sorry for the noise.
>>
>> 在 2021/12/28 20:54, Baokun Li 写道:
>>> When we mount a jffs2 image, assume that the first few blocks of
>>> the image are normal and contain at least one xattr-related inode,
>>> but the next block is abnormal. As a result, an error is returned
>>> in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then
>>> called in jffs2_build_filesystem() and then again in
>>> jffs2_do_fill_super().
>>>
>>> Finally we can observe the following report:
>>>    ==================================================================
>>>    BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac
>>>    Read of size 8 at addr ffff8881243384e0 by task mount/719
>>>
>>>    Call Trace:
>>>     dump_stack+0x115/0x16b
>>>     jffs2_clear_xattr_subsystem+0x95/0x6ac
>>>     jffs2_do_fill_super+0x84f/0xc30
>>>     jffs2_fill_super+0x2ea/0x4c0
>>>     mtd_get_sb+0x254/0x400
>>>     mtd_get_sb_by_nr+0x4f/0xd0
>>>     get_tree_mtd+0x498/0x840
>>>     jffs2_get_tree+0x25/0x30
>>>     vfs_get_tree+0x8d/0x2e0
>>>     path_mount+0x50f/0x1e50
>>>     do_mount+0x107/0x130
>>>     __se_sys_mount+0x1c5/0x2f0
>>>     __x64_sys_mount+0xc7/0x160
>>>     do_syscall_64+0x45/0x70
>>>     entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>>    Allocated by task 719:
>>>     kasan_save_stack+0x23/0x60
>>>     __kasan_kmalloc.constprop.0+0x10b/0x120
>>>     kasan_slab_alloc+0x12/0x20
>>>     kmem_cache_alloc+0x1c0/0x870
>>>     jffs2_alloc_xattr_ref+0x2f/0xa0
>>>     jffs2_scan_medium.cold+0x3713/0x4794
>>>     jffs2_do_mount_fs.cold+0xa7/0x2253
>>>     jffs2_do_fill_super+0x383/0xc30
>>>     jffs2_fill_super+0x2ea/0x4c0
>>>    [...]
>>>
>>>    Freed by task 719:
>>>     kmem_cache_free+0xcc/0x7b0
>>>     jffs2_free_xattr_ref+0x78/0x98
>>>     jffs2_clear_xattr_subsystem+0xa1/0x6ac
>>>     jffs2_do_mount_fs.cold+0x5e6/0x2253
>>>     jffs2_do_fill_super+0x383/0xc30
>>>     jffs2_fill_super+0x2ea/0x4c0
>>>    [...]
>>>
>>>    The buggy address belongs to the object at ffff8881243384b8
>>>     which belongs to the cache jffs2_xattr_ref of size 48
>>>    The buggy address is located 40 bytes inside of
>>>     48-byte region [ffff8881243384b8, ffff8881243384e8)
>>>    [...]
>>>    ==================================================================
>>>
>>> The triggering of the BUG is shown in the following stack:
>>> -----------------------------------------------------------
>>> jffs2_fill_super
>>>     jffs2_do_fill_super
>>>       jffs2_do_mount_fs
>>>         jffs2_build_filesystem
>>>           jffs2_scan_medium
>>>             jffs2_scan_eraseblock        <--- ERROR
>>>           jffs2_clear_xattr_subsystem    <--- free
>>>       jffs2_clear_xattr_subsystem        <--- free again
>>> -----------------------------------------------------------
>>>
>>> An error is returned in jffs2_do_mount_fs(). If the error is returned
>>> by jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to
>>> be executed. If the error is returned by jffs2_build_filesystem(), the
>>> jffs2_clear_xattr_subsystem() also does not need to be executed again.
>>> So move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root'
>>> to fix this UAF problem.
>>>
>>> Fixes: aa98d7cf59b5 ("[JFFS2][XATTR] XATTR support on JFFS2 (version. 5)")
>>> Cc: stable@vger.kernel.org
>>> Reported-by: Hulk Robot <hulkci@huawei.com>
>>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> Applied. Thanks for fixing!
>
> Thanks,
> //richard
> .


Thank you for your review!

-- 
With Best Regards,
Baokun Li