Re: [PATCH-next] nbd: fix incomplete validation of ioctl arg

[zhongjinghua <zhongjinghua@huaweicloud.com>]

ping...

Hello

Anyone looking this？

在 2023/3/14 15:10, zhongjinghua 写道:
> ping...
>
> Hello
>
> Anyone looking this？
>
> 在 2023/2/6 22:58, Zhong Jinghua 写道:
>> We tested and found an alarm caused by nbd_ioctl arg without 
>> verification.
>> The UBSAN warning calltrace like below:
>>
>> UBSAN: Undefined behaviour in fs/buffer.c:1709:35
>> signed integer overflow:
>> -9223372036854775808 - 1 cannot be represented in type 'long long int'
>> CPU: 3 PID: 2523 Comm: syz-executor.0 Not tainted 4.19.90 #1
>> Hardware name: linux,dummy-virt (DT)
>> Call trace:
>>   dump_backtrace+0x0/0x3f0 arch/arm64/kernel/time.c:78
>>   show_stack+0x28/0x38 arch/arm64/kernel/traps.c:158
>>   __dump_stack lib/dump_stack.c:77 [inline]
>>   dump_stack+0x170/0x1dc lib/dump_stack.c:118
>>   ubsan_epilogue+0x18/0xb4 lib/ubsan.c:161
>>   handle_overflow+0x188/0x1dc lib/ubsan.c:192
>>   __ubsan_handle_sub_overflow+0x34/0x44 lib/ubsan.c:206
>>   __block_write_full_page+0x94c/0xa20 fs/buffer.c:1709
>>   block_write_full_page+0x1f0/0x280 fs/buffer.c:2934
>>   blkdev_writepage+0x34/0x40 fs/block_dev.c:607
>>   __writepage+0x68/0xe8 mm/page-writeback.c:2305
>>   write_cache_pages+0x44c/0xc70 mm/page-writeback.c:2240
>>   generic_writepages+0xdc/0x148 mm/page-writeback.c:2329
>>   blkdev_writepages+0x2c/0x38 fs/block_dev.c:2114
>>   do_writepages+0xd4/0x250 mm/page-writeback.c:2344
>>
>> The reason for triggering this warning is __block_write_full_page()
>> -> i_size_read(inode) - 1 overflow.
>> inode->i_size is assigned in __nbd_ioctl() -> nbd_set_size() -> 
>> bytesize.
>> We think it is necessary to limit the size of arg to prevent errors.
>>
>> Moreover, __nbd_ioctl() -> nbd_add_socket(), arg will be cast to int.
>> Assuming the value of arg is 0x80000000000000001) (on a 64-bit machine),
>> it will become 1 after the coercion, which will return unexpected 
>> results.
>>
>> Fix it by adding checks to prevent passing in too large numbers.
>>
>> Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
>> ---
>>   drivers/block/nbd.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index 592cfa8b765a..e1c954094b6c 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -325,6 +325,9 @@ static int nbd_set_size(struct nbd_device *nbd, 
>> loff_t bytesize,
>>       if (blk_validate_block_size(blksize))
>>           return -EINVAL;
>>   +    if (bytesize < 0)
>> +        return -EINVAL;
>> +
>>       nbd->config->bytesize = bytesize;
>>       nbd->config->blksize_bits = __ffs(blksize);
>>   @@ -1111,6 +1114,9 @@ static int nbd_add_socket(struct nbd_device 
>> *nbd, unsigned long arg,
>>       struct nbd_sock *nsock;
>>       int err;
>>   +    /* Arg will be cast to int, check it to avoid overflow */
>> +    if (arg > INT_MAX)
>> +        return -EINVAL;
>>       sock = nbd_get_socket(nbd, arg, &err);
>>       if (!sock)
>>           return err;