Re: [PATCH v12 2/3] ipc: Conserve sequence numbers in ipcmni_extend mode

From: Waiman Long <longman@redhat.com>
To: Manfred Spraul <manfred@colorfullife.com>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-doc@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
	Matthew Wilcox <willy@infradead.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Takashi Iwai <tiwai@suse.de>, Davidlohr Bueso <dbueso@suse.de>,
	1vier1@web.de
Subject: Re: [PATCH v12 2/3] ipc: Conserve sequence numbers in ipcmni_extend mode
Date: Mon, 18 Mar 2019 14:57:47 -0400	[thread overview]
Message-ID: <c66181f7-e19e-0764-9de7-6bcefaef398a@redhat.com> (raw)
In-Reply-To: <398a8bcb-7568-0a5b-c6cb-77420de445b9@colorfullife.com>

On 03/16/2019 02:52 PM, Manfred Spraul wrote:
> Hi,
>
> On 2/28/19 7:47 PM, Waiman Long wrote:
>> @@ -216,10 +221,11 @@ static inline int ipc_idr_alloc(struct ipc_ids
>> *ids, struct kern_ipc_perm *new)
>>        */
>>         if (next_id < 0) { /* !CHECKPOINT_RESTORE or next_id is unset */
>> -        new->seq = ids->seq++;
>> -        if (ids->seq > IPCID_SEQ_MAX)
>> -            ids->seq = 0;
>>           idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT);
>> +        if ((idx <= ids->last_idx) && (++ids->seq > IPCID_SEQ_MAX))
>> +            ids->seq = 0;
>
> I'm always impressed by such lines:
>
> Everything in just two lines, use "++a", etc.
>
> But: How did you test it?
>
> idr_alloc() can fail, the code doesn't handle that :-(
>
>

You are right. I should have checked for the error case.

Thanks for spotting that.

Cheers,
Longman