[tip: efi/urgent] firmware/efi: Fix a use after bug in efi_mem_reserve_persistent

["tip-bot2 for Lv Yunlong" <tip-bot2@linutronix.de>]

The following commit has been merged into the efi/urgent branch of tip:

Commit-ID:     9ceee7d0841a8f7d7644021ba7d4cc1fbc7966e3
Gitweb:        https://git.kernel.org/tip/9ceee7d0841a8f7d7644021ba7d4cc1fbc7966e3
Author:        Lv Yunlong <lyl2019@mail.ustc.edu.cn>
AuthorDate:    Wed, 10 Mar 2021 00:31:27 -08:00
Committer:     Ard Biesheuvel <ardb@kernel.org>
CommitterDate: Fri, 19 Mar 2021 07:44:27 +01:00

firmware/efi: Fix a use after bug in efi_mem_reserve_persistent

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 <lyl2019@mail.ustc.edu.cn>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/efi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index df3f9bc..4b7ee3f 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -927,7 +927,7 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
 	}
 
 	/* 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(phys_addr_t addr, u64 size)
 			memunmap(rsv);
 			return efi_mem_reserve_iomem(addr, size);
 		}
+		prsv = rsv->next;
 		memunmap(rsv);
 	}