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Tue, 26 Mar 2024 11:19:48 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap1.dmz-prg2.suse.org with ESMTPSA id cSodGVSvAmbiDgAAD6G6ig (envelope-from ); Tue, 26 Mar 2024 11:19:48 +0000 Date: Tue, 26 Mar 2024 12:19:50 +0100 Message-ID: <87msqlutnt.wl-tiwai@suse.de> From: Takashi Iwai To: Duoming Zhou Cc: linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, tiwai@suse.com, perex@perex.cz Subject: Re: [PATCH v2] ALSA: sh: aica: reorder cleanup operations to avoid UAF bugs In-Reply-To: <20240326094238.95442-1-duoming@zju.edu.cn> References: <20240326094238.95442-1-duoming@zju.edu.cn> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 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-Level: Authentication-Results: smtp-out2.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=Nanpw0Nl; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=SNN5bTqH X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-2.18 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_FIVE(0.00)[5]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+]; MX_GOOD(-0.01)[]; MID_CONTAINS_FROM(1.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; NEURAL_HAM_SHORT(-0.20)[-1.000]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-1.67)[92.96%] X-Spam-Score: -2.18 X-Rspamd-Queue-Id: A17215CC2A X-Spam-Flag: NO On Tue, 26 Mar 2024 10:42:38 +0100, Duoming Zhou wrote: > > The dreamcastcard->timer could schedule the spu_dma_work and the > spu_dma_work could also arm the dreamcastcard->timer. > > When the snd_pcm_substream is closing, the aica_channel will be > deallocated. But it could still be dereferenced in the worker > thread. The reason is that del_timer() will return directly > regardless of whether the timer handler is running or not and > the worker could be rescheduled in the timer handler. As a result, > the UAF bug will happen. The racy situation is shown below: > > (Thread 1) | (Thread 2) > snd_aicapcm_pcm_close() | > ... | run_spu_dma() //worker > | mod_timer() > flush_work() | > del_timer() | aica_period_elapsed() //timer > kfree(dreamcastcard->channel) | schedule_work() > | run_spu_dma() //worker > ... | dreamcastcard->channel-> //USE > > In order to mitigate this bug and other possible corner cases, > call mod_timer() conditionally in run_spu_dma(), then implement > PCM sync_stop op to cancel both the timer and worker. The sync_stop > op will be called from PCM core appropriately when needed. > > Fixes: 198de43d758c ("[ALSA] Add ALSA support for the SEGA Dreamcast PCM device") > Suggested-by: Takashi Iwai > Signed-off-by: Duoming Zhou > --- > Changes in v2: > - call mod_timer() conditionally and implement PCM sync_stop op. Thanks, applied now. Takashi