CVE-2024-57876

In the Linux kernel, the following vulnerability has been resolved:

drm/dp_mst: Fix resetting msg rx state after topology removal

If the MST topology is removed during the reception of an MST down reply or MST up request sideband message, the drmdpmsttopologymgr::upreqrecv/downreprecv states could be reset from one thread via drmdpmsttopologymgrsetmst(false), racing with the reading/parsing of the message from another thread via drmdpmsthandledownrep() or drmdpmsthandleupreq(). The race is possible since the reader/parser doesn't hold any lock while accessing the reception state. This in turn can lead to a memory corruption in the reader/parser as described by commit bd2fccac61b4 ("drm/dp_mst: Fix MST sideband message body length check").

Fix the above by resetting the message reception state if needed before reading/parsing a message. Another solution would be to hold the drmdpmsttopologymgr::lock for the whole duration of the message reception/parsing in drmdpmsthandledownrep() and drmdpmsthandleupreq(), however this would require a bigger change. Since the fix is also needed for stable, opting for the simpler solution in this patch.