nbd: fix incomplete validation of ioctl arg

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 <[email protected]>
Reviewed-by: Yu Kuai <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: philzjh

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;