Re: [PATCH v2 4/5] bug: Provide toggle for BUG on data corruption

[Joe Perches]

On Tue, 2016-08-16 at 17:20 -0700, Kees Cook wrote:
> The kernel checks for cases of data structure corruption under some
> CONFIGs (e.g. CONFIG_DEBUG_LIST). When corruption is detected, some
> systems may want to BUG() immediately instead of letting the system run
> with known corruption.  Usually these kinds of manipulation primitives can
> be used by security flaws to gain arbitrary memory write control. This
> provides a new config CONFIG_BUG_ON_DATA_CORRUPTION and a corresponding
> macro CHECK_DATA_CORRUPTION for handling these situations. Notably, even
> if not BUGing, the kernel should not continue processing the corrupted
> structure.
[]
> diff --git a/include/linux/bug.h b/include/linux/bug.h
[]
> @@ -118,4 +118,21 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
>  }
>  
>  #endif	/* CONFIG_GENERIC_BUG */
> +
> +/*
> + * Since detected data corruption should stop operation on the affected
> + * structures, this returns false if the corruption condition is found.
> + */
> +#define CHECK_DATA_CORRUPTION(condition, format...)			 \

My preference would be to use (condition, fmt, ...)

> +	do {								 \
> +		if (unlikely(condition)) {				 \
> +			if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
> +				printk(KERN_ERR format);		 \

and
				pr_err(fmt, ##__VA_ARGS__);

so that any use would also get any local pr_fmt applied as well.

> +				BUG();					 \
> +			} else						 \
> +				WARN(1, format);			 \
> +			return false;					 \
> +		}							 \
> +	} while (0)
> +
>  #endif	/* _LINUX_BUG_H */