linux-kernel - Re: [PATCH] block: Fix potential NULL pointer dereference in __bio_crypt

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Date:   Wed, 2 Sep 2020 01:56:53 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     Eric Biggers <ebiggers@...nel.org>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "satyat@...gle.com" <satyat@...gle.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: Fix potential NULL pointer dereference in
 __bio_crypt_clone()

Eric Biggers <ebiggers@...nel.org> wrote:
>On Tue, Sep 01, 2020 at 07:59:21AM -0400, Miaohe Lin wrote:
>> mempool_alloc() may return NULL if __GFP_DIRECT_RECLAIM is not set in 
>> gfp_mask under memory pressure. So we should check the return value of
>> mempool_alloc() against NULL before dereference.
>> 
>> Fixes: a892c8d52c02 ("block: Inline encryption support for blk-mq")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>
>It's intended that __GFP_DIRECT_RECLAIM always be set here.
>Do you have an example where it isn't set here?

map_request() only pass GFP_ATOMIC to gfp_mask, though bio crypt is not used yet.

>Also, if this can indeed happen, then we need to make __bio_crypt_clone() (and bio_crypt_clone()) return a bool (or an error code) to indicate whether it succeeded or failed.  We can't just ignore the allocation failure.
>
>- Eric

IMO, just the allocation failure is ok or we would break KABI.
Many thanks.