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Tue, 20 Oct 2026 10:16:27 +0000 From: Takashi Iwai To: linux-sound@vger.kernel.org Cc: linux-kernel@vger.kernel.org Subject: [PATCH 1/2] ALSA: emux: Fix UAF of soundfont zones at note-on Date: Tue, 20 Oct 2026 12:16:20 +0200 Message-ID: <20261020101624.205638-1-tiwai@suse.de> X-Mailer: git-send-email 2.55.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -2.80 X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,sashiko.dev:url,suse.de:email]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_NONE(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[] snd_emux_note_on() looks up the matching zones via snd_soundfont_search_zone(), which takes sflist->lock only during the lookup and returns the raw zone pointers after releasing it. The caller then stores them in vp->zone without any protection. Meanwhile, a concurrent SNDRV_EMUX_IOCTL_REMOVE_LAST_SAMPLES ioctl may unlink and free those zones in snd_soundfont_remove_unlocked(); this leads to a use-after-free in snd_emux_note_on(), and later at accessing the cached vp->zone, e.g. in snd_emux_send_effect(). Fix it by holding sflist->lock in snd_emux_note_on() over the whole zone lookup and voice setup, and let snd_soundfont_search_zone() require the caller to hold the lock, instead. snd_soundfont_lock_preset() takes sflist->lock for setting presets_locked, so the removal path now syncs with the note-on finish. Reported-by: Sashiko Closes: https://sashiko.dev/#/bug/linux-697212bb-a434-4ff5-8778-25a84f5dad89 Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai --- sound/synth/emux/emux_synth.c | 3 +++ sound/synth/emux/soundfont.c | 9 ++++++--- 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/sound/synth/emux/emux_synth.c b/sound/synth/emux/emux_synth.c index 6982e1317da5..2cbf12364a1e 100644 --- a/sound/synth/emux/emux_synth.c +++ b/sound/synth/emux/emux_synth.c @@ -60,6 +60,9 @@ snd_emux_note_on(void *p, int note, int vel, struct snd_midi_channel *chan) return; key = note; /* remember the original note */ + + /* hold sflist->lock for protecting against concurrent free */ + guard(spinlock_irqsave)(&emu->sflist->lock); nvoices = get_zone(emu, port, ¬e, vel, chan, table); if (! nvoices) return; diff --git a/sound/synth/emux/soundfont.c b/sound/synth/emux/soundfont.c index c172b53b17a4..039357d96e07 100644 --- a/sound/synth/emux/soundfont.c +++ b/sound/synth/emux/soundfont.c @@ -1225,6 +1225,9 @@ delete_preset(struct snd_sf_list *sflist, struct snd_sf_zone *zp) * The found zones are stored on 'table' array. max_layers defines * the maximum number of elements in this array. * This function returns the number of found zones. 0 if not found. + * + * The caller must hold sflist->lock, and keep holding it as long as + * the returned zones are accessed. */ int snd_soundfont_search_zone(struct snd_sf_list *sflist, int *notep, int vel, @@ -1234,11 +1237,11 @@ snd_soundfont_search_zone(struct snd_sf_list *sflist, int *notep, int vel, { int nvoices; - /* this function is supposed to be called atomically, - * so we check the lock. if it's busy, just returns 0 to + lockdep_assert_held(&sflist->lock); + + /* if the presets are being modified, just returns 0 to * tell the caller the busy state */ - guard(spinlock_irqsave)(&sflist->lock); if (sflist->presets_locked) return 0; nvoices = search_zones(sflist, notep, vel, preset, bank, -- 2.55.0