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Sun, 1 Nov 2026 15:32:35 +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 1MkkFJNb52qQLgAAD6G6ig (envelope-from ); Sun, 01 Nov 2026 15:32:35 +0000 Date: Sun, 01 Nov 2026 16:32:35 +0100 Message-ID: <87ld7cpnxo.wl-tiwai@suse.de> From: Takashi Iwai To: YuanZhe Liu <25031212351@stu.xidian.edu.cn> Cc: Jaroslav Kysela , Takashi Iwai , Bin Yu , Cheng Wen , linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v3] ALSA: bcd2000: Fix use-after-free of MIDI URBs on file close In-Reply-To: <20261031190936.5696-1-25031212351@stu.xidian.edu.cn> References: <874ie1rbge.wl-tiwai@suse.de> <20261031190936.5696-1-25031212351@stu.xidian.edu.cn> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: F14F51F7BD X-Spam-Level: X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spamd-Result: default: False [-12.51 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_TLS_ALL(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; RCVD_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Score: -12.51 On Sat, 31 Oct 2026 20:09:36 +0100, YuanZhe Liu wrote: > > bcd2000_disconnect() calls snd_card_disconnect(), which only prevents > new opens, and then frees the MIDI URBs. A rawmidi file that was > already open can still be closed afterwards, and its close callback, > bcd2000_midi_output_close(), calls usb_kill_urb() on midi_out_urb. > > The URB pointers are cleared on disconnect and their accesses are > serialized with midi_lock, but bcd2000_midi_output_close() reads > midi_out_urb without that lock. The check can therefore pass just > before the pointer is cleared, and usb_kill_urb() then runs on the URB > that has already been freed: > > BUG: KASAN: slab-use-after-free in usb_kill_urb+0x74/0x80 > Read of size 8 at addr ffff8880078e7d40 > usb_kill_urb > bcd2000_midi_output_close > close_substream > rawmidi_release_priv > snd_rawmidi_release > > Allocated by: usb_alloc_urb <- bcd2000_init_midi <- bcd2000_probe > Freed by: usb_free_urb <- bcd2000_midi_free > <- bcd2000_disconnect > > Take the lock in bcd2000_midi_output_close() and reference the URB with > usb_get_urb() before releasing it. The URB then stays valid until > usb_put_urb() after usb_kill_urb() has returned, even if a disconnect > frees it in the meantime. usb_kill_urb() itself cannot run under > midi_lock, as the completion handler takes the same lock. > > Fixes: b47a22290d58 ("ALSA: MIDI driver for Behringer BCD2000 USB device") > Cc: stable@vger.kernel.org > Signed-off-by: YuanZhe Liu <25031212351@stu.xidian.edu.cn> Applied now. Thanks. Takashi