[PATCH v2 RESEND] fs: cramfs_fs.h: Fix shifting signed 32-bit value by 31 bits problem

[PATCH v2 RESEND] fs: cramfs_fs.h: Fix shifting signed 32-bit value by 31 bits problem

[Puranjay Mohan]

Fix CRAMFS_BLK_FLAG_UNCOMPRESSED to use "U" cast to avoid shifting signed
32-bit value by 31 bits problem. This isn't a problem for kernel builds
with gcc.

This could be problem since this header is part of public API which
could be included for builds using compilers that don't handle this
condition safely resulting in undefined behavior.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
---
V2 - use the unsigned constants for all flags, not just one
RESEND - Added Nicolas Pitre to CC list, added reviewed by tags.

 include/uapi/linux/cramfs_fs.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/cramfs_fs.h b/include/uapi/linux/cramfs_fs.h
index 6713669aa2ed..71cb602d4198 100644
--- a/include/uapi/linux/cramfs_fs.h
+++ b/include/uapi/linux/cramfs_fs.h
@@ -98,8 +98,8 @@ struct cramfs_super {
  *
  * That leaves room for 3 flag bits in the block pointer table.
  */
-#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1 << 31)
-#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1 << 30)
+#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1U << 31)
+#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1U << 30)
 
 #define CRAMFS_BLK_FLAGS	( CRAMFS_BLK_FLAG_UNCOMPRESSED \
 				| CRAMFS_BLK_FLAG_DIRECT_PTR )
-- 
2.21.0

Re: [PATCH v2 RESEND] fs: cramfs_fs.h: Fix shifting signed 32-bit value by 31 bits problem

[Nicolas Pitre]

On Tue, 18 Jun 2019, Puranjay Mohan wrote:

> Fix CRAMFS_BLK_FLAG_UNCOMPRESSED to use "U" cast to avoid shifting signed
> 32-bit value by 31 bits problem. This isn't a problem for kernel builds
> with gcc.
> 
> This could be problem since this header is part of public API which
> could be included for builds using compilers that don't handle this
> condition safely resulting in undefined behavior.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

Acked-by: Nicolas Pitre <nico@fluxnic.net>



> ---
> V2 - use the unsigned constants for all flags, not just one
> RESEND - Added Nicolas Pitre to CC list, added reviewed by tags.
> 
>  include/uapi/linux/cramfs_fs.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/cramfs_fs.h b/include/uapi/linux/cramfs_fs.h
> index 6713669aa2ed..71cb602d4198 100644
> --- a/include/uapi/linux/cramfs_fs.h
> +++ b/include/uapi/linux/cramfs_fs.h
> @@ -98,8 +98,8 @@ struct cramfs_super {
>   *
>   * That leaves room for 3 flag bits in the block pointer table.
>   */
> -#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1 << 31)
> -#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1 << 30)
> +#define CRAMFS_BLK_FLAG_UNCOMPRESSED	(1U << 31)
> +#define CRAMFS_BLK_FLAG_DIRECT_PTR	(1U << 30)
>  
>  #define CRAMFS_BLK_FLAGS	( CRAMFS_BLK_FLAG_UNCOMPRESSED \
>  				| CRAMFS_BLK_FLAG_DIRECT_PTR )
> -- 
> 2.21.0
> 
>