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Subject: Re: [PATCH v1] qnx4_match: do not over run the buffer
From:   Tong Zhang <ztong0001@gmail.com>
In-Reply-To: <2474566.rpppqFFLNx@alarsen.net>
Date:   Sat, 21 Nov 2020 16:47:24 -0500
Cc:     linux-kernel@vger.kernel.org
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Message-Id: <E554952E-602B-4711-BEF1-FB3398DA7225@gmail.com>
References: <20201120212120.2502522-1-ztong0001@gmail.com>
 <2474566.rpppqFFLNx@alarsen.net>
To:     Anders Larsen <al@alarsen.net>
Precedence: bulk


> On Nov 21, 2020, at 4:40 PM, Anders Larsen <al@alarsen.net> wrote:
>=20
> On Friday, 2020-11-20 22:21 Tong Zhang wrote:
>> the di_fname may not terminated by '\0', use strnlen to prevent =
buffer
>> overrun
>>=20
>> ---
>> fs/qnx4/namei.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>=20
>> 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 =3D QNX4_SHORT_NAME_MAX;
>> 	}
>> -	thislen =3D strlen( de->di_fname );
>> +	thislen =3D strnlen( de->di_fname, QNX4_SHORT_NAME_MAX );
>=20
> that should be
> +	thislen =3D strnlen( de->di_fname, namelen );
> otherwise the length of a filename would always be limited to =
QNX4_SHORT_NAME_MAX (16) characters.
>=20
Why should we put something bigger here if the size of =
qnx4_inode_entry->di_fname is QNX4_SHORT_NAME_MAX.
Won=E2=80=99t that be a problem?

>> 	if ( thislen > namelen )
>> 		thislen =3D namelen;
>=20
> These two lines can be dropped now, as the result of strnlen() cannot =
exceed namelen anyway.
>=20
> Cheers
> Anders
>=20
>=20