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

[Yu Kuai]

在 2023/02/06 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.

Looks good to me, feel free to add:

Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> Signed-off-by: Zhong Jinghua <zhongjinghua@xxxxxxxxxx>
> ---
>   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;