vm_phys: Check `RB_FIND()` return value in case it is NULL

When trying to unregister a fictitious range in
`vm_phys_fictitious_unreg_range()`, the function checks the properties
of the looked up segment, but it does not check if a segment was found
in the first place.

This can happen with the amdgpu DRM driver which could call
`vm_phys_fictitious_unreg_range()` without a fictitious range registered
if the initialisation of the driver failed (for example because
firmwares are unavailable).

The code in the DRM driver was improved to avoid that, but
`vm_phys_fictitious_unreg_range()` should still check the return value
of `RB_FIND()` before trying to dereference the segment pointer and
panic with a page fault.

Reviewed by:	emaste
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55076

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/vm/vm_phys.c b/sys/vm/vm_phys.c
index ba16ae551093..1737020436c6 100644
--- a/sys/vm/vm_phys.c
+++ b/sys/vm/vm_phys.c
@@ -1213,7 +1213,7 @@ vm_phys_fictitious_unreg_range(vm_paddr_t start, vm_paddr_t end)
 
 	rw_wlock(&vm_phys_fictitious_reg_lock);
 	seg = RB_FIND(fict_tree, &vm_phys_fictitious_tree, &tmp);
-	if (seg->start != start || seg->end != end) {
+	if (seg == NULL || seg->start != start || seg->end != end) {
 		rw_wunlock(&vm_phys_fictitious_reg_lock);
 		panic(
 		    "Unregistering not registered fictitious range [%#jx:%#jx]",