Re: [PATCH] block: Fix potential NULL pointer dereference in __bio_crypt_clone()

[linmiaohe]

Eric Biggers <ebiggers@xxxxxxxxxx> 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@xxxxxxxxxx>
>
>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.