From: Oliver Neukum Date: Wed, 4 Mar 2026 13:01:12 +0000 (+0100) Subject: usb: class: cdc-wdm: fix reordering issue in read code path X-Git-Tag: v7.0-rc4~14^2~17 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8df672bfe3ec2268c2636584202755898e547173;p=thirdparty%2Flinux.git usb: class: cdc-wdm: fix reordering issue in read code path 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") Cc: stable Signed-off-by: Oliver Neukum Closes: https://lore.kernel.org/linux-usb/CALbr=LbrUZn_cfp7CfR-7Z5wDTHF96qeuM=3fO2m-q4cDrnC4A@mail.gmail.com/ Reported-by: Gui-Dong Han Reviewed-by: Gui-Dong Han Link: https://patch.msgid.link/20260304130116.1721682-1-oneukum@suse.com Signed-off-by: Greg Kroah-Hartman --- 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: