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Wed, 11 Nov 2026 08:56:54 +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 jJ+0NtUt9GpNMwAAD6G6ig (envelope-from ); Wed, 11 Nov 2026 08:56:54 +0000 Date: Wed, 11 Nov 2026 09:56:53 +0100 Message-ID: <87ld6zu4oa.wl-tiwai@suse.de> From: Takashi Iwai To: Sreeraj S Kurup Cc: tiwai@suse.de, linux-kernel@vger.kernel.org, linux-sound@vger.kernel.org, perex@perex.cz, tiwai@suse.com Subject: Re: [PATCH v3] ALSA: control: Validate element info in compat ioctl In-Reply-To: <20261110160510.2697-1-sreekuttan2156239@gmail.com> References: <87y0b1ug39.wl-tiwai@suse.de> <20261110160510.2697-1-sreekuttan2156239@gmail.com> 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-Spamd-Result: default: False [-12.30 / 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]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[6]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -12.30 X-Spam-Level: X-Spam-Flag: NO On Tue, 10 Nov 2026 17:05:10 +0100, Sreeraj S Kurup wrote: > > Hi Takashi, > > The validation in snd_ctl_elem_write() happens too late. Before calling > snd_ctl_elem_write(), the compat handler calls copy_ctl_value_from_user(), which > uses the type and count returned by get_ctl_type() to determine how many values to copy. > > If the control's info callback returns an invalid count, the integer and boolean paths > can access beyond the fixed-size integer value array. Other paths can also calculate a > copy size larger than the available kernel buffer. > > The read path has a similar issue. It uses the same type and count when copying the values > back to userspace, which can result in an out-of-bounds read from the kernel buffer. > > So, validation in snd_ctl_elem_write() cannot prevent these problems because the unsafe > accesses can happen before it is called. > > Using __snd_ctl_elem_info() in get_ctl_type() ensures that the type and count are validated > before they are used by the compat handlers. It also reuses the existing element ID handling > and access checks. > > Therefore, I think this validation is necessary. OK, it makes sense. Now applied to for-next branch. thanks, Takashi