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commit8df672bfe3upstream. 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:afba937e54("USB: CDC WDM driver") Cc: stable <stable@kernel.org> Signed-off-by: Oliver Neukum <oneukum@suse.com> Closes: https://lore.kernel.org/linux-usb/CALbr=LbrUZn_cfp7CfR-7Z5wDTHF96qeuM=3fO2m-q4cDrnC4A@mail.gmail.com/ Reported-by: Gui-Dong Han <hanguidong02@gmail.com> Reviewed-by: Gui-Dong Han <hanguidong02@gmail.com> Link: https://patch.msgid.link/20260304130116.1721682-1-oneukum@suse.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>