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Subject: Re: [PATCH][udf-next] udf: don't call mark_buffer_dirty on a null bh pointer
From:   Steve Magnani <steve.magnani@digidescorp.com>
In-Reply-To: <20190220095015.GB27474@quack2.suse.cz>
Date:   Wed, 20 Feb 2019 05:27:34 -0600
Cc:     Colin King <colin.king@canonical.com>, Jan Kara <jack@suse.com>,
        kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
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Message-Id: <C9E129B8-B914-4E9B-8AAF-76C64E9D8F8B@digidescorp.com>
References: <20190219114403.24771-1-colin.king@canonical.com> <20190219140240.GA31849@quack2.suse.cz> <aef899da-4dc1-1e40-30c9-fc2ca87f2380@digidescorp.com> <20190220095015.GB27474@quack2.suse.cz>
To:     Jan Kara <jack@suse.cz>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Feb 20, 2019, at 3:50 AM, Jan Kara <jack@suse.cz> wrote:
>=20
>> On Tue 19-02-19 08:17:09, Steve Magnani wrote:
>>> On 2/19/19 8:02 AM, Jan Kara wrote:
>>>> On Tue 19-02-19 11:44:03, Colin King wrote:
>>>> From: Colin Ian King <colin.king@canonical.com>
>>>>=20
>>>> There is a null check on the pointer bh to avoid a null pointer derefer=
ence
>>>> on bh->b_data however later bh is passed to mark_buffer_dirty that can a=
lso
>>>> cause a null pointer dereference on bh.  Avoid this potential null poin=
ter
>>>> dereference by moving the call to mark_buffer_dirty inside the null che=
cked
>>>> block.
>>>>=20
>>>> Fixes: e8b4274735e4 ("udf: finalize integrity descriptor before writeba=
ck")
>>>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>>> Thanks for the patch! In fact it is the 'if (bh)' check that's
>>> unnecessarily defensive (we cannot have sbi->s_lvid_dirty and
>>> !sbi->s_lvid_bh). So I'll just drop that check (attached patch).
>>>=20
>>>                                Honza
>>>=20
>>>> ---
>>>>  fs/udf/super.c | 12 ++++++------
>>>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>>>=20
>>>> diff --git a/fs/udf/super.c b/fs/udf/super.c
>>>> index a6940d90bedd..b7e9a83d39db 100644
>>>> --- a/fs/udf/super.c
>>>> +++ b/fs/udf/super.c
>>>> @@ -2336,13 +2336,13 @@ static int udf_sync_fs(struct super_block *sb, i=
nt wait)
>>>>              lvid =3D (struct logicalVolIntegrityDesc *)bh->b_data;
>>>>              udf_finalize_lvid(lvid);
>>>> -        }
>>>> -        /*
>>>> -         * Blockdevice will be synced later so we don't have to submit=

>>>> -         * the buffer for IO
>>>> -         */
>>>> -        mark_buffer_dirty(bh);
>>>> +            /*
>>>> +             * Blockdevice will be synced later so we don't have
>>>> +             * to submit the buffer for IO
>>>> +             */
>>>> +            mark_buffer_dirty(bh);
>>>> +        }
>>>>          sbi->s_lvid_dirty =3D 0;
>>>>      }
>>>>      mutex_unlock(&sbi->s_alloc_mutex);
>>>> --=20
>>>> 2.20.1
>>>>=20
>> Reviewed-by: Steven J. Magnani <steve@digidescorp.com>
>=20
> Is this Reviewed-by for my fixup or the Colin's? Because I've decided to
> rather remove the 'if (bh)' check completely since it is pointless...
>=20
>                                Honza
> --=20

Sorry, I realized on rereading that this could be ambiguous. The R-B is for y=
our patch.

Steve=