libcamera: shared_mem_object: Prevent memfd from shrinking or growing

The memfd underlying the SharedMem object must not shrink, or memory
corruption will happen. Prevent this by setting the shrink seal on the
file. As there's no valid use case for growing the memory either, set
the grow seal as well.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Milan Zamazal <mzamazal@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

src/libcamera/shared_mem_object.cpp

@@ -58,7 +58,8 @@ SharedMem::SharedMem() = default;
  */
 SharedMem::SharedMem(const std::string &name, std::size_t size)
 {
-	UniqueFD memfd = MemFd::create(name.c_str(), size);
+	UniqueFD memfd = MemFd::create(name.c_str(), size, MemFd::Seal::Shrink |
+				       MemFd::Seal::Grow);
 	if (!memfd.isValid())
 		return;