linux-kernel - Re: [PATCH] NFS: remove unneeded check in decode_devicenotify

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Message-ID: <ea3c96de-cf01-fd50-5a21-01b07293e922@ispras.ru>
Date:   Wed, 16 Feb 2022 20:44:07 +0300
From:   Alexey Khoroshilov <khoroshilov@...ras.ru>
To:     Anna Schumaker <anna@...nel.org>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] NFS: remove unneeded check in decode_devicenotify_args()

Hi Anna,

On 16.02.2022 18:30, Anna Schumaker wrote:
> On Tue, Feb 15, 2022 at 5:17 AM Alexey Khoroshilov
> <khoroshilov@...ras.ru> wrote:
>>
>> Overflow check in not needed anymore after we switch to kmalloc_array().
> 
> Don't we still need the overflow check since 'n' is used in the
> for-loop end condition farther down in this function?


It is not, because it will be detected by kmalloc_array(), it returns
NULL and we will go out before the loop:

	args->devs = kmalloc_array(n, sizeof(*args->devs), GFP_KERNEL);
	if (!args->devs) {
		status = htonl(NFS4ERR_DELAY);
		goto out;
	}

Best regards,
Alexey


>>
>> Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
>> Fixes: a4f743a6bb20 ("NFSv4.1: Convert open-coded array allocation calls to kmalloc_array()")
>> ---
>>  fs/nfs/callback_xdr.c | 4 ----
>>  1 file changed, 4 deletions(-)
>>
>> diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
>> index f90de8043b0f..8dcb08e1a885 100644
>> --- a/fs/nfs/callback_xdr.c
>> +++ b/fs/nfs/callback_xdr.c
>> @@ -271,10 +271,6 @@ __be32 decode_devicenotify_args(struct svc_rqst *rqstp,
>>         n = ntohl(*p++);
>>         if (n == 0)
>>                 goto out;
>> -       if (n > ULONG_MAX / sizeof(*args->devs)) {
>> -               status = htonl(NFS4ERR_BADXDR);
>> -               goto out;
>> -       }
>>
>>         args->devs = kmalloc_array(n, sizeof(*args->devs), GFP_KERNEL);
>>         if (!args->devs) {
>> --
>> 2.7.4
>>