Re: [PATCH -next v3] nbd: add the check to prevent overflow in __nbd_ioctl()

From: Josef Bacik
Date: Fri Aug 13 2021 - 11:53:56 EST

On 8/3/21 10:12 PM, Baokun Li wrote:
If user specify a large enough value of NBD blocks option, it may trigger
signed integer overflow which may lead to nbd->config->bytesize becomes a
large or small value, zero in particular.

UBSAN: Undefined behaviour in drivers/block/nbd.c:325:31
signed integer overflow:
1024 * 4611686155866341414 cannot be represented in type 'long long int'
Call trace:
handle_overflow+0x188/0x1dc lib/ubsan.c:192
__ubsan_handle_mul_overflow+0x34/0x44 lib/ubsan.c:213
nbd_size_set drivers/block/nbd.c:325 [inline]
__nbd_ioctl drivers/block/nbd.c:1342 [inline]
nbd_ioctl+0x998/0xa10 drivers/block/nbd.c:1395
__blkdev_driver_ioctl block/ioctl.c:311 [inline]

Although it is not a big deal, still silence the UBSAN by limit
the input value.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Use check_mul_overflow().
The check_mul_overflow function requires the same input parameter type.

drivers/block/nbd.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index c38317979f74..5a42b838d26c 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1384,6 +1384,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
unsigned int cmd, unsigned long arg)
struct nbd_config *config = nbd->config;
+ loff_t bytesize;
switch (cmd) {
@@ -1398,8 +1399,11 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
return nbd_set_size(nbd, arg, config->blksize);
- return nbd_set_size(nbd, arg * config->blksize,
- config->blksize);
+ if (unlikely(check_mul_overflow((loff_t)arg,
+ config->blksize,
+ &bytesize)))
+ return -EINVAL;
+ return nbd_set_size(nbd, bytesize, config->blksize);

The unlikely isn't needed here, just makes it harder to read the thing, drop it and then you can add

Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>