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R. Silva" Cc: Jaroslav Kysela , Takashi Iwai , Jussi Kivilinna , alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH][next] ALSA: 6fire: Fix undefined behavior bug in struct comm_runtime In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Message-ID-Hash: GIROX636W45ZBLNZX6EAGDKQHYXY5QN5 X-Message-ID-Hash: GIROX636W45ZBLNZX6EAGDKQHYXY5QN5 X-MailFrom: tiwai@suse.de X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-alsa-devel.alsa-project.org-0; header-match-alsa-devel.alsa-project.org-1; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.8 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Fri, 29 Sep 2023 17:59:22 +0200, Gustavo A. R. Silva wrote: > > `struct urb` is a flexible structure, which means that it contains a > flexible-array member at the bottom. This could potentially lead to an > overwrite of the objects following `receiver` in `struct comm_runtime`, > among them some function pointers. > > Fix this by placing the declaration of object `receiver` at the end of > `struct comm_runtime`. > > Fixes: ddb6b5a96437 ("ALSA: 6fire: fix DMA issues with URB transfer_buffer usage") > Cc: stable@vger.kernel.org > Signed-off-by: Gustavo A. R. Silva Sorry for the late reply, as I've been (still) off since the last week. Through a quick glance, I don't mind much to apply this, but I still wonder how this "fixes" anything. Does it silence compiler warnings or such? Certainly struct urb *may* have flex array, but in this case, it's clearly not used, so it's fixed-size. And, even if we shuffle the member to put to the last, it doesn't fix anything automagically alone. If a flex array were used, it still leads to memory corruption unless we implement the allocation properly. So I find the patch description is somehow misleading. thanks, Takashi > --- > sound/usb/6fire/comm.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/sound/usb/6fire/comm.h b/sound/usb/6fire/comm.h > index 2447d7ecf179..ee81572a4eec 100644 > --- a/sound/usb/6fire/comm.h > +++ b/sound/usb/6fire/comm.h > @@ -19,7 +19,6 @@ enum /* settings for comm */ > struct comm_runtime { > struct sfire_chip *chip; > > - struct urb receiver; > u8 *receiver_buffer; > > u8 serial; /* urb serial */ > @@ -30,6 +29,7 @@ struct comm_runtime { > int (*write8)(struct comm_runtime *rt, u8 request, u8 reg, u8 value); > int (*write16)(struct comm_runtime *rt, u8 request, u8 reg, > u8 vh, u8 vl); > + struct urb receiver; > }; > > int usb6fire_comm_init(struct sfire_chip *chip); > -- > 2.34.1 >