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Wed, 5 Aug 2026 07:36:14 +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 xYKSEu7ncmooRAAAD6G6ig (envelope-from ); Wed, 05 Aug 2026 07:36:14 +0000 Date: Wed, 05 Aug 2026 09:36:13 +0200 Message-ID: <87ik5pggsy.wl-tiwai@suse.de> From: Takashi Iwai To: Baul Lee Cc: perex@perex.cz, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com, stable@vger.kernel.org Subject: Re: [PATCH] ALSA: usx2y: bound the hwdep mmap fault offset In-Reply-To: <20260805013445.38283-1-baul.lee@xbow.com> References: <20260805013445.38283-1-baul.lee@xbow.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 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-Spamd-Result: default: False [-3.51 / 50.00]; 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)[-0.996]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[xbow.com:email,suse.de:mid,suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Flag: NO X-Spam-Score: -3.51 X-Spam-Level: X-Rspamd-Queue-Id: 802157F82F X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action On Wed, 05 Aug 2026 03:34:45 +0200, Baul Lee wrote: > > snd_us428ctls_vm_fault() turns the faulting page offset into a kernel > address with no bound of any kind: > > offset = vmf->pgoff << PAGE_SHIFT; > vaddr = (char *)(...)->us428ctls_sharedmem + offset; > page = virt_to_page(vaddr); > get_page(page); > vmf->page = page; > > return 0; > > snd_us428ctls_mmap() checks only the length of the mapping, never the > offset, and us428ctls_sharedmem is a single page from > alloc_pages_exact(). For a character device file_mmap_size_max() > returns ULONG_MAX, so the mm layer imposes no ceiling either. Every page > offset above zero resolves to a struct page outside the object, and the > handler installs it into the caller's address space read-write; the vma > is not marked read-only. > > The caller picks the page frame with a single mmap() argument and gets > read-write access to a page of kernel memory it does not own; an offset > that lands in an unpopulated vmemmap region oopses instead. > > A process that can open the hwdep node of an attached US-X2Y reaches > this after loading the FPGA image through the same node; no capability > check is involved. > > On 7.2.0-rc5 (arm64), mmap() with a large offset: > > Unable to handle kernel paging request at virtual address fffffdffc45d5ac8 > pc : snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y] > Call trace: > snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y] > __do_fault > __handle_mm_fault > handle_mm_fault > el0_da > > Reject any offset outside the shared region. The pcm hwdep handler in > usx2yhwdeppcm.c computes its address the same way and needs the same > bound. > > Discovered by XBOW, triaged by Baul Lee > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Reported-by: Federico Kirschbaum > Reported-by: Baul Lee > Cc: stable@vger.kernel.org > Signed-off-by: Baul Lee Applied now. Thanks. Takashi