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Sun, 26 Jul 2026 07:06:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Ivb0GOexZWqPAgAAD6G6ig (envelope-from ); Sun, 26 Jul 2026 07:06:15 +0000 Date: Sun, 26 Jul 2026 09:06:15 +0200 Message-ID: <878q6yb57c.wl-tiwai@suse.de> From: Takashi Iwai To: Baul Lee Cc: linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, perex@perex.cz, tiwai@suse.com, lina+kernel@asahilina.net, federico.kirschbaum@xbow.com, stable@vger.kernel.org Subject: Re: [PATCH] ALSA: usb-audio: fix stack info leak in RME Digiface status In-Reply-To: <20260726065020.46070-1-baul.lee@xbow.com> References: <20260726065020.46070-1-baul.lee@xbow.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Score: -1.80 X-Spam-Level: X-Spam-Flag: NO X-Spamd-Result: default: False [-1.80 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MIME_TRACE(0.00)[0:+]; TAGGED_RCPT(0.00)[kernel]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[xbow.com:email,suse.de:mid] On Sun, 26 Jul 2026 08:50:20 +0200, Baul Lee wrote: > > snd_rme_digiface_read_status() reads a four-word status block from the > device into an uninitialised on-stack __le32 buf[4] and, whenever the > vendor control-IN transfer does not return a negative error, copies all > four words into the caller's status[]. > > snd_usb_ctl_msg() copies the full requested size back into the caller's > buffer regardless of how many bytes the data stage actually delivered: > > buf = kmemdup(data, size, GFP_KERNEL); > err = usb_control_msg(dev, pipe, request, requesttype, > value, index, buf, size, timeout); > memcpy(data, buf, size); > > usb_control_msg() returns the transferred length on a short control-IN, > which is a non-negative value, and writes only that many bytes. The > remainder of the copy back is the kmemdup()ed image of the caller's > buffer, so a device answering with a short data stage leaves the > trailing words of buf[] holding leftover kernel stack. The only guard > in the caller is err < 0, so those words are stored into status[]. > > They then reach user space: snd_rme_digiface_get_status_val() selects a > 16-bit halfword of status[] per the control's reg/mask, and the eight > Digiface status controls together expose the whole 16-byte frame to an > unprivileged reader of /dev/snd/controlC*. > > Zero-initialise the buffer so a short read yields zeros instead of stack > residue. This mirrors snd_rme_get_status1(), which already clears its > output word before the same kind of vendor read. > > Discovered by XBOW, triaged by Baul Lee > > Fixes: 611a96f6acf2 ("ALSA: usb-audio: Add mixer quirk for RME Digiface USB") > Reported-by: Federico Kirschbaum > Reported-by: Baul Lee > Cc: stable@vger.kernel.org > Signed-off-by: Baul Lee Applied now. Thanks. Takashi