linux-kernel - Re: [PATCH] block: Replace bio_check_ro()'s WARN

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Message-ID: <201911221052.0FDE1A1@keescook>
Date:   Fri, 22 Nov 2019 10:53:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     syzbot+21cfe1f803e0e158acf1@...kaller.appspotmail.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: Replace bio_check_ro()'s WARN_ON()

Friendly ping! I keep tripping over this. Can this please get applied so
we can silence syzbot and avoid needless WARNs? :)

-Kees

On Fri, Aug 24, 2018 at 02:15:35PM -0700, Kees Cook wrote:
> As described in commit 96c6a32ccb55a ("include/asm-generic/bug.h: clarify
> valid uses of WARN()"), this replaces a userspace-reachable WARN_ON()
> with pr_warn_once(). The reachability is even noted in the existing
> comment. This appears to be an "expected by unlikely" condition, so
> getting rid of the WARN_ON() means kernel fuzzers will stop reporting
> the problem. Additionally un-breaks the error string so it can more
> easily be found with grep.
> 
> Reported-by: syzbot+21cfe1f803e0e158acf1@...kaller.appspotmail.com
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: linux-block@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  block/blk-core.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index dee56c282efb..470c3cea8cb0 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2166,11 +2166,9 @@ static inline bool bio_check_ro(struct bio *bio, struct hd_struct *part)
>  	if (part->policy && (op_is_write(op) && !op_is_flush(op))) {
>  		char b[BDEVNAME_SIZE];
>  
> -		WARN_ONCE(1,
> -		       "generic_make_request: Trying to write "
> -			"to read-only block-device %s (partno %d)\n",
> +		/* Older lvm-tools actually triggers this. */
> +		pr_warn_once("Trying to write to read-only block-device %s (partno %d)\n",
>  			bio_devname(bio, b), part->partno);
> -		/* Older lvm-tools actually trigger this */
>  		return false;
>  	}
>  
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook
> Pixel Security

-- 
Kees Cook