Re: linux-next: build failure after merge of the kspp tree

[Kees Cook <keescook@chromium.org>]

On Tue, Jan 25, 2022 at 11:57:57AM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the kspp tree, today's linux-next build (x86_64
> allmodconfig) failed like this:
> 
> In file included from include/linux/string.h:253,
>                  from include/linux/bitmap.h:11,
>                  from include/linux/cpumask.h:12,
>                  from arch/x86/include/asm/cpumask.h:5,
>                  from arch/x86/include/asm/msr.h:11,
>                  from arch/x86/include/asm/processor.h:22,
>                  from arch/x86/include/asm/cpufeature.h:5,
>                  from arch/x86/include/asm/thread_info.h:53,
>                  from include/linux/thread_info.h:60,
>                  from arch/x86/include/asm/preempt.h:7,
>                  from include/linux/preempt.h:78,
>                  from include/linux/spinlock.h:55,
>                  from include/linux/wait.h:9,
>                  from include/linux/mempool.h:8,
>                  from include/linux/bio.h:8,
>                  from fs/btrfs/ioctl.c:7:
> In function 'fortify_memcpy_chk',
>     inlined from 'btrfs_ioctl_encoded_write' at fs/btrfs/ioctl.c:5082:3:
> include/linux/fortify-string.h:316:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>   316 |                         __write_overflow_field(p_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/fortify-string.h:324:25: error: call to '__read_overflow2_field' declared with attribute warning: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror=attribute-warning]
>   324 |                         __read_overflow2_field(q_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> Caused by commit
> 
>   602670289b69 ("fortify: Detect struct member overflows in memcpy() at compile-time")
> 
> interacting with commit
> 
>   504e1ebb6316 ("btrfs: add BTRFS_IOC_ENCODED_WRITE")
> 
> from the btrfs tree.

Thanks!

I found the btrfs patch here:
https://lore.kernel.org/all/ec08e6f559ab47b3300ca5a67e8fc984fd3f040f.1637179348.git.osandov@fb.com/

> 
> I applied the following hack:
> 
> From: Stephen Rothwell <sfr@canb.auug.org.au>
> Date: Tue, 25 Jan 2022 11:47:17 +1100
> Subject: [PATCH] fix up for "btrfs: add BTRFS_IOC_ENCODED_WRITE"
> 
> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
> ---
>  fs/btrfs/ioctl.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 73ad918a05a9..d34620034f8e 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -5079,9 +5079,14 @@ static int btrfs_ioctl_encoded_write(struct file *file, void __user *argp,
>  		}
>  		args.iov = compat_ptr(args32.iov);
>  		args.iovcnt = args32.iovcnt;
> -		memcpy(&args.offset, &args32.offset,
> -		       sizeof(args) -
> -		       offsetof(struct btrfs_ioctl_encoded_io_args, offset));
> +		args.offset = args32.offset;
> +		args.flags = args32.flags;
> +		args.len = args32.len;
> +		args.unencoded_len = args32.unencoded_len;
> +		args.unencoded_offset = args32.unencoded_offset;
> +		args.compression = args32.compression;
> +		args.encryption = args32.encryption;
> +		memcpy(args.reserved, args32.reserved, sizeof(args.reserved));
>  #else
>  		return -ENOTTY;
>  #endif

I'll see if I can construct something shorter using struct_group().

-Kees

-- 
Kees Cook