linux-kernel - Re: Explanation on Uninitialized Variable bio in blk_rq_prep

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Message-ID: <6a0ec577-fba1-44b3-87d8-3a202df19d8c@oracle.com>
Date: Fri, 4 Oct 2024 15:33:00 +0100
From: John Garry <john.g.garry@...cle.com>
To: SurajSonawane2415 <surajsonawane0215@...il.com>, hch@...radead.org
Cc: axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Explanation on Uninitialized Variable bio in blk_rq_prep_clone

On 04/10/2024 15:10, SurajSonawane2415 wrote:
> Explaination of how bio could be used uninitialized in this function:
> 
> In the function blk_rq_prep_clone, the variable bio is declared but can remain uninitialized
> if the allocation with bio_alloc_clone fails. This can lead to undefined behavior when the
> function attempts to free bio in the error handling section using bio_put(bio).
> By initializing bio to NULL at declaration, we ensure that the cleanup code will only
> interact with bio if it has been successfully allocated.
> 
>

What about if rq_src->bio is NULL for blk_rq_prep_clone() -> 
__rq_for_each_bio(,rq_src):

#define __rq_for_each_bio(_bio, rq)	\
	if ((rq->bio))			\
		for (_bio = (rq)->bio; _bio; _bio = _bio->bi_next)

Then I don't think bio it get init'ed. Whether this is possible 
(rq_src->bio is NULL) is another question.