linux-kernel - Re: [PATCH][udf-next] udf: don't call mark_buffer

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Date:   Tue, 19 Feb 2019 15:02:40 +0100
From:   Jan Kara <jack@...e.cz>
To:     Colin King <colin.king@...onical.com>
Cc:     Jan Kara <jack@...e.com>, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][udf-next] udf: don't call mark_buffer_dirty on a null bh
 pointer

On Tue 19-02-19 11:44:03, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> There is a null check on the pointer bh to avoid a null pointer dereference
> on bh->b_data however later bh is passed to mark_buffer_dirty that can also
> cause a null pointer dereference on bh.  Avoid this potential null pointer
> dereference by moving the call to mark_buffer_dirty inside the null checked
> block.
> 
> Fixes: e8b4274735e4 ("udf: finalize integrity descriptor before writeback")
> Signed-off-by: Colin Ian King <colin.king@...onical.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).

								Honza

> ---
>  fs/udf/super.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> 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, int wait)
>  
>  			lvid = (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 = 0;
>  	}
>  	mutex_unlock(&sbi->s_alloc_mutex);
> -- 
> 2.20.1
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-udf-Drop-pointless-check-from-udf_sync_fs.patch" of type "text/x-patch" (1241 bytes)