linux-kernel - Re: [PATCH v1] qnx4_match: do not over run the buffer

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Date:   Sat, 21 Nov 2020 16:47:24 -0500
From:   Tong Zhang <ztong0001@...il.com>
To:     Anders Larsen <al@...rsen.net>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] qnx4_match: do not over run the buffer


> On Nov 21, 2020, at 4:40 PM, Anders Larsen <al@...rsen.net> wrote:
> 
> On Friday, 2020-11-20 22:21 Tong Zhang wrote:
>> the di_fname may not terminated by '\0', use strnlen to prevent buffer
>> overrun
>> 
>> ---
>> fs/qnx4/namei.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
>> index 8d72221735d7..c0e79094f578 100644
>> --- a/fs/qnx4/namei.c
>> +++ b/fs/qnx4/namei.c
>> @@ -40,7 +40,7 @@ static int qnx4_match(int len, const char *name,
>> 	} else {
>> 		namelen = QNX4_SHORT_NAME_MAX;
>> 	}
>> -	thislen = strlen( de->di_fname );
>> +	thislen = strnlen( de->di_fname, QNX4_SHORT_NAME_MAX );
> 
> that should be
> +	thislen = strnlen( de->di_fname, namelen );
> otherwise the length of a filename would always be limited to QNX4_SHORT_NAME_MAX (16) characters.
> 
Why should we put something bigger here if the size of qnx4_inode_entry->di_fname is QNX4_SHORT_NAME_MAX.
Won’t that be a problem?

>> 	if ( thislen > namelen )
>> 		thislen = namelen;
> 
> These two lines can be dropped now, as the result of strnlen() cannot exceed namelen anyway.
> 
> Cheers
> Anders
> 
>