Re: [PATCH 5.14 018/334] nbd: add the check to prevent overflow in __nbd_ioctl()

[Naresh Kamboju]

On Mon, 13 Sept 2021 at 19:51, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Baokun Li <libaokun1@xxxxxxxxxx>
>
> [ Upstream commit fad7cd3310db3099f95dd34312c77740fbc455e5 ]
>
> 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>
> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20210804021212.990223-1-libaokun1@xxxxxxxxxx
> [axboe: dropped unlikely()]
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  drivers/block/nbd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 19f5d5a8b16a..acf3f85bf3c7 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1388,6 +1388,7 @@ 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) {
>         case NBD_DISCONNECT:
> @@ -1402,8 +1403,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>         case NBD_SET_SIZE:
>                 return nbd_set_size(nbd, arg, config->blksize);
>         case NBD_SET_SIZE_BLOCKS:
> -               return nbd_set_size(nbd, arg * config->blksize,
> -                                   config->blksize);
> +               if (check_mul_overflow((loff_t)arg, config->blksize, &bytesize))
> +                       return -EINVAL;
> +               return nbd_set_size(nbd, bytesize, config->blksize);
>         case NBD_SET_TIMEOUT:
>                 nbd_set_cmd_timeout(nbd, arg);
>                 return 0;

arm clang-10, clang-11, clang-12 and clang-13 builds failed.
due to this commit on 5.14 and 5.13 on following configs,
  - footbridge_defconfig
  - mini2440_defconfig
  - s3c2410_defconfig

This was already reported on the mailing list.

ERROR: modpost: "__mulodi4" [drivers/block/nbd.ko] undefined! #1438
https://github.com/ClangBuiltLinux/linux/issues/1438

[PATCH 00/10] raise minimum GCC version to 5.1
https://lore.kernel.org/lkml/20210910234047.1019925-1-ndesaulniers@xxxxxxxxxx/

linux-next: build failure while building Linus' tree
https://lore.kernel.org/all/20210909182525.372ee687@xxxxxxxxxxxxxxxx/

Full build log,
https://gitlab.com/Linaro/lkft/mirrors/stable/linux-stable-rc/-/jobs/1585407346#L1111


--
Linaro LKFT
https://lkft.linaro.org