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Mon, 19 Oct 2026 18:06:08 +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 ibkgFBBc1mrqTQAAD6G6ig (envelope-from ); Mon, 19 Oct 2026 18:06:08 +0000 Date: Mon, 19 Oct 2026 20:06:08 +0200 Message-ID: <87tsmhimzz.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: perex@perex.cz, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH] ALSA: aloop: Keep the timer source alive until card release In-Reply-To: References: 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-Action: no action X-Spam-Score: -3.51 X-Spam-Flag: NO X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; 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)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[perex.cz,suse.com,vger.kernel.org,gmail.com]; RCPT_COUNT_SEVEN(0.00)[7]; FROM_EQ_ENVFROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Level: X-Rspamd-Queue-Id: C5DD41F44E X-Rspamd-Server: rspamd2.dmz-prg2.suse.org On Mon, 19 Oct 2026 11:06:13 +0200, Cen Zhang wrote: > > The timer_source string must remain valid while PCM opens can select > and parse it. loopback_set_timer_source() allocates the string with > parent-device devres, which can release it while the card is still > registered. > > A successful nonempty proc replacement after snd_card_register() adds > the string allocation after trigger_card_free. Unbinding the platform > device while snd_aloop remains loaded releases devres in reverse order. > An open for an unused cable can run after the string is freed and before > the card-free action disconnects the card: > > Device unbind PCM open > devres_release_all() > free replacement string > snd_pcm_open() > snd_card_file_add() > loopback_open() > loopback_snd_timer_open() > loopback_parse_timer_id() > trigger_card_free() > snd_card_free() > snd_card_disconnect() > > The parser can then read freed memory. KASAN has reported a one-byte > use-after-free read in strchr() from loopback_snd_timer_open(). The > cable_lock mutex serializes explicit replacements with opens, but > implicit devres release does not take it. The card and module references > held by PCM open do not retain this separate devres allocation. > > Use kstrdup() and release the current string from card->private_free. > PCM admission already retains the card until each file is removed, and > card disconnect drains proc callbacks before final card release. This > keeps the string alive across admitted PCM opens and preserves the > cable_lock serialization of replacements. Install the callback before > the initial allocation so probe failures also release the string. > > Fixes: b072e65aadd6 ("ALSA: aloop: Allocate resources with device-managed APIs") > Signed-off-by: Cen Zhang > Assisted-by: LLM Applied now. Thanks. Takashi