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Sat, 31 Oct 2026 16:10:06 +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 ZGQ2DN4S5mrxNgAAD6G6ig (envelope-from ); Sat, 31 Oct 2026 16:10:06 +0000 Date: Sat, 31 Oct 2026 17:10:05 +0100 Message-ID: <87pkwprgv6.wl-tiwai@suse.de> From: Takashi Iwai To: Dmitriy Chumachenko Cc: Jaroslav Kysela , Takashi Iwai , Greg Kroah-Hartman , Sasha Levin , Oswald Buddenhagen , Mehul Rao , Ji'an Zhou , Norbert Szetei , , , Subject: Re: [PATCH] ALSA: pcm: Don't WARN on NULL dma_area in the default mmap fault handler In-Reply-To: <20261030112502.22227-1-Dmitry.Chumachenko@cyberprotect.ru> References: <20261030112502.22227-1-Dmitry.Chumachenko@cyberprotect.ru> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 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 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: F229F222F1 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)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; URIBL_BLOCKED(0.00)[suse.de:dkim,cyberprotect.ru:email,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCPT_COUNT_TWELVE(0.00)[12]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com,gmx.de]; FREEMAIL_CC(0.00)[perex.cz,suse.com,linuxfoundation.org,kernel.org,gmx.de,gmail.com,doyensec.com,alsa-project.org,vger.kernel.org,linuxtesting.org]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from] X-Spam-Score: -12.51 On Fri, 30 Oct 2026 12:25:02 +0100, Dmitriy Chumachenko wrote: > > During fuzz testing, the following issue was discovered. > > WARNING: CPU: 2 PID: 1734 at sound/core/pcm_native.c:3835 > snd_pcm_mmap_data_fault+0x47f/0x530 sound/core/pcm_native.c:3835 > > Modules linked in: > CPU: 2 PID: 1734 Comm: syz.1.352 Not tainted 6.1.187-syzkaller-00593-g063a81552262 #0 > RIP: 0010:snd_pcm_mmap_data_fault+0x47f/0x530 sound/core/pcm_native.c:3835 > > Call Trace: > > __do_fault+0x10d/0x480 mm/memory.c:4280 > do_cow_fault mm/memory.c:4661 [inline] > do_fault+0xa7a/0x1100 mm/memory.c:4762 > handle_pte_fault mm/memory.c:5031 [inline] > __handle_mm_fault+0xdf3/0x2e40 mm/memory.c:5173 > handle_mm_fault+0x2da/0xa60 mm/memory.c:5294 > do_user_addr_fault+0x4aa/0x1050 arch/x86/mm/fault.c:1338 > handle_page_fault arch/x86/mm/fault.c:1429 [inline] > exc_page_fault+0x98/0x1b0 arch/x86/mm/fault.c:1482 > asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:608 > > snd_pcm_mmap_data_fault() guards the default RAM-buffer path with > WARN_ON_ONCE(!runtime->dma_area). As commit d2913a07d903 notes, a driver > may allow mmap before dma_area is set up, so this state is reachable from > user space: mmap the PCM data region and fault it while the buffer is not > allocated. The WARN then fires on a user-triggerable path and panics a > kernel with panic_on_warn. > > Drop the WARN; the NULL check and VM_FAULT_SIGBUS return stay, which is > the correct silent handling. > > Fixes: d2913a07d903 ("ALSA: pcm: Add sanity NULL check for the default mmap fault handler") > Signed-off-by: Dmitriy Chumachenko The WARN_ON() was put there because it shouldn't happen, and dropping WARN_ON() is likely an incorrect "solution". Could you rather investigate how this is triggered (under which condition with which driver)? That should be addressed instead of just silencing it. thanks, Takashi