efi: fix panic in kdump kernel

jira LE-1907
cve CVE-2024-35800
Rebuild_History Non-Buildable kernel-5.14.0-427.31.1.el9_4
commit-author Oleksandr Tymoshenko <ovt@google.com>
commit 62b71cd

Check if get_next_variable() is actually valid pointer before
calling it. In kdump kernel this method is set to NULL that causes
panic during the kexec-ed kernel boot.

Tested with QEMU and OVMF firmware.

Fixes: bad267f ("efi: verify that variable services are supported")
	Signed-off-by: Oleksandr Tymoshenko <ovt@google.com>
	Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
(cherry picked from commit 62b71cd)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

drivers/firmware/efi/efi.c

@@ -200,6 +200,8 @@ static bool generic_ops_supported(void)
 
 	name_size = sizeof(name);
 
+	if (!efi.get_next_variable)
+		return false;
 	status = efi.get_next_variable(&name_size, &name, &guid);
 	if (status == EFI_UNSUPPORTED)
 		return false;