Re: [PATCH v2] md/md-multipath: guard against a possible NULL dereference

[Yu Kuai]

Hi,

在 2023/04/21 14:21, Daniil Tatianin 写道:
> mempool_alloc might fail to allocate a slot, in which case we will end
> up dereferencing a NULL mp_bh pointer.
>
> Found by Linux Verification Center (linuxtesting.org) with the SVACE
> static analysis tool.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>
> ---
> Changes since v1: fixed a typo
> ---
>   drivers/md/md-multipath.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
> index 66edf5e72bd6..8dfa353440e5 100644
> --- a/drivers/md/md-multipath.c
> +++ b/drivers/md/md-multipath.c
> @@ -108,6 +108,8 @@ static bool multipath_make_request(struct mddev *mddev, struct bio * bio)
>   		return true;
>   
>   	mp_bh = mempool_alloc(&conf->pool, GFP_NOIO);

The comment in mempool_alloc says:

Note that due to preallocation, this function *never* fails when called
from process contexts.

And there are many places to use this way, so I think this patch is not
needed.

Thanks,
Kuai
> +	if (!mp_bh)
> +		return false;
>   
>   	mp_bh->master_bio = bio;
>   	mp_bh->mddev = mddev;