[PATCH 5.10 155/157] firmware/efi: Fix a use after bug in efi_mem_reserve_persistent

[Greg Kroah-Hartman]

From: Lv Yunlong <lyl2...@mail.ustc.edu.cn>

commit 9ceee7d0841a8f7d7644021ba7d4cc1fbc7966e3 upstream.

In the for loop in efi_mem_reserve_persistent(), prsv = rsv->next
use the unmapped rsv. Use the unmapped pages will cause segment
fault.

Fixes: 18df7577adae6 ("efi/memreserve: deal with memreserve entries in unmapped 
memory")
Signed-off-by: Lv Yunlong <lyl2...@mail.ustc.edu.cn>
Signed-off-by: Ard Biesheuvel <a...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/firmware/efi/efi.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -927,7 +927,7 @@ int __ref efi_mem_reserve_persistent(phy
        }
 
        /* first try to find a slot in an existing linked list entry */
-       for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
+       for (prsv = efi_memreserve_root->next; prsv; ) {
                rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
                index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
                if (index < rsv->size) {
@@ -937,6 +937,7 @@ int __ref efi_mem_reserve_persistent(phy
                        memunmap(rsv);
                        return efi_mem_reserve_iomem(addr, size);
                }
+               prsv = rsv->next;
                memunmap(rsv);
        }