AZL-91326

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

drm/amd/display: Avoid NULL dereference in dcdmubsrv error paths

In dcdmubsrvlogdiagnosticdata() and dcdmubsrvenabledpiatrace().

Both functions check:

if (!dcdmubsrv || !dcdmubsrv->dmub)

and then call DCLOGERROR() inside that block.

DCLOGERROR() uses dcdmubsrv->ctx internally. So if dcdmubsrv is NULL, the logging itself can dereference a NULL pointer and cause a crash.

Fix this by splitting the checks.

First check if dcdmubsrv is NULL and return immediately. Then check dcdmubsrv->dmub and log the error only when dcdmubsrv is valid.

Fixes the below: ../display/dc/dcdmubsrv.c:962 dcdmubsrvlogdiagnosticdata() error: we previously assumed 'dcdmubsrv' could be null (see line 961) ../display/dc/dcdmubsrv.c:1167 dcdmubsrvenabledpiatrace() error: we previously assumed 'dcdmubsrv' could be null (see line 1166)