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SubjectRe: [PATCH-next] nbd: fix incomplete validation of ioctl arg
From
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;

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