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Wed, 4 Mar 2026 13:01:23 +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 f1JqLiMtqGkSNAAAD6G6ig (envelope-from ); Wed, 04 Mar 2026 13:01:23 +0000 From: Oliver Neukum To: gregkh@linuxfoundation.org, hanguidong02@gmail.com, linux-usb@vger.kernel.org Cc: Oliver Neukum Subject: [PATCH] usb: class: cdc-wdm: fix reordering issue in read code path Date: Wed, 4 Mar 2026 14:01:12 +0100 Message-ID: <20260304130116.1721682-1-oneukum@suse.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Score: -2.80 X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-0.998]; MIME_GOOD(-0.10)[text/plain]; TO_MATCH_ENVRCPT_ALL(0.00)[]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:mid,suse.com:email]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FREEMAIL_TO(0.00)[linuxfoundation.org,gmail.com,vger.kernel.org]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; FREEMAIL_ENVRCPT(0.00)[gmail.com] X-Spam-Flag: NO Quoting the bug report: Due to compiler optimization or CPU out-of-order execution, the desc->length update can be reordered before the memmove. If this happens, wdm_read() can see the new length and call copy_to_user() on uninitialized memory. This also violates LKMM data race rules [1]. Fix it by using WRITE_ONCE and memory barriers. Fixes: afba937e540c9 ("USB: CDC WDM driver") Signed-off-by: Oliver Neukum --- drivers/usb/class/cdc-wdm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c index f2d94cfc70af..7556c0dac908 100644 --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -225,7 +225,8 @@ static void wdm_in_callback(struct urb *urb) /* we may already be in overflow */ if (!test_bit(WDM_OVERFLOW, &desc->flags)) { memmove(desc->ubuf + desc->length, desc->inbuf, length); - desc->length += length; + smp_wmb(); /* against wdm_read() */ + WRITE_ONCE(desc->length, desc->length + length); } } skip_error: @@ -533,6 +534,7 @@ static ssize_t wdm_read return -ERESTARTSYS; cntr = READ_ONCE(desc->length); + smp_rmb(); /* against wdm_in_callback() */ if (cntr == 0) { desc->read = 0; retry: -- 2.53.0