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Subject: Re: [PATCH 1/2] fibmap: Warn and return an error in case of block >
 INT_MAX
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jan Kara <jack@suse.com>, tytso@mit.edu,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        linux-ext4@vger.kernel.org
References: <cover.1587670914.git.riteshh@linux.ibm.com>
 <e34d1ac05d29aeeb982713a807345a0aaafc7fe0.1587670914.git.riteshh@linux.ibm.com>
 <20200424191739.GA217280@gmail.com>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Sat, 25 Apr 2020 04:24:24 +0530
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On 4/25/20 12:47 AM, Eric Biggers wrote:
> On Fri, Apr 24, 2020 at 12:52:17PM +0530, Ritesh Harjani wrote:
>> We better warn the fibmap user and not return a truncated and therefore
>> an incorrect block map address if the bmap() returned block address
>> is greater than INT_MAX (since user supplied integer pointer).
>>
>> It's better to WARN all user of ioctl_fibmap() and return a proper error
>> code rather than silently letting a FS corruption happen if the user tries
>> to fiddle around with the returned block map address.
>>
>> We fix this by returning an error code of -ERANGE and returning 0 as the
>> block mapping address in case if it is > INT_MAX.
>>
>> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
>> ---
>>   fs/ioctl.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/fs/ioctl.c b/fs/ioctl.c
>> index f1d93263186c..3489f3a12c1d 100644
>> --- a/fs/ioctl.c
>> +++ b/fs/ioctl.c
>> @@ -71,6 +71,11 @@ static int ioctl_fibmap(struct file *filp, int __user *p)
>>   	block = ur_block;
>>   	error = bmap(inode, &block);
>>   
>> +	if (block > INT_MAX) {
>> +		error = -ERANGE;
>> +		WARN(1, "would truncate fibmap result\n");
>> +	}
>> +
> 
> WARN() is only for kernel bugs.  This case would be a userspace bug, not a
> kernel bug, right?  If so, it should use pr_warn(), not WARN().

Ok, I see.
Let me replace WARN() with below pr_warn() line then. If no objections,
then will send this in a v2 with both patches combined as Darrick
suggested. - (with Reviewed-by tags of Jan & Christoph).

pr_warn("fibmap: this would truncate fibmap result\n");


> 
> - Eric
>