2021-09-27 09:45:41

by Arnd Bergmann

Subject: [PATCH] loop: avoid out-of-range warning

From: Arnd Bergmann <[email protected]>

clang warns that the sanity check for page size always succeeds
when building with 64KB pages:

drivers/block/loop.c:282:27: error: result of comparison of constant 65536 with expression of type 'unsigned short' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
~~~~~ ^ ~~~~~~~~~

There is nothing wrong here, so just shut up the check by changing
the type of the bsize argument.

Fixes: 3448914e8cc5 ("loop: Add LOOP_CONFIGURE ioctl")
Signed-off-by: Arnd Bergmann <[email protected]>
---
drivers/block/loop.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7bf4686af774..51315a93b399 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -277,7 +277,7 @@ static void __loop_update_dio(struct loop_device *lo, bool dio)
* @bsize: size to validate
*/
static int
-loop_validate_block_size(unsigned short bsize)
+loop_validate_block_size(unsigned int bsize)
{
if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
return -EINVAL;
--
2.29.2

2021-09-27 09:53:54

by Martijn Coenen

Subject: Re: [PATCH] loop: avoid out-of-range warning

Thanks!

On Mon, Sep 27, 2021 at 11:43 AM Arnd Bergmann <[email protected]> wrote:
>
> From: Arnd Bergmann <[email protected]>
>
> clang warns that the sanity check for page size always succeeds
> when building with 64KB pages:
>
> drivers/block/loop.c:282:27: error: result of comparison of constant 65536 with expression of type 'unsigned short' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
> if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
> ~~~~~ ^ ~~~~~~~~~
>
> There is nothing wrong here, so just shut up the check by changing
> the type of the bsize argument.
>
> Fixes: 3448914e8cc5 ("loop: Add LOOP_CONFIGURE ioctl")
> Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Martijkn Coenen <[email protected]>

> ---
> drivers/block/loop.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 7bf4686af774..51315a93b399 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -277,7 +277,7 @@ static void __loop_update_dio(struct loop_device *lo, bool dio)
> * @bsize: size to validate
> */
> static int
> -loop_validate_block_size(unsigned short bsize)
> +loop_validate_block_size(unsigned int bsize)
> {
> if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
> return -EINVAL;
> --
> 2.29.2
>

2021-09-27 11:19:00

by Tetsuo Handa

Subject: Re: [PATCH] loop: avoid out-of-range warning

Well, you found a bug here.

lo_simple_ioctl(LOOP_SET_BLOCK_SIZE) passes "unsigned long arg" to
loop_validate_block_size() via loop_set_block_size(), and uses only
lower 32bits. "(lo->lo_queue->limits.logical_block_size == arg)" is
failing to "return 0;" if lower 32bits are the same but higher 32bits
are not 0. Shouldn't we also check that higher 32bits are 0, by either
making loop_validate_block_size() to accept "unsigned long" or making
loop_set_block_size() return -EINVAL if larger than UINT_MAX ?

> There is nothing wrong here, so just shut up the check by changing
> the type of the bsize argument.

I think there is something wrong here.
Since "unsigned short bsize" checked only lower 16bits, a fuzzer can
pass e.g. 0xDEAD0200 (which is not a is_power_of_2() 32bits value) to

blk_queue_logical_block_size(lo->lo_queue, arg);
blk_queue_physical_block_size(lo->lo_queue, arg);
blk_queue_io_min(lo->lo_queue, arg);

and confuse the system?