From d7fe913f23b1907ac6ccb1552151fbcaa89bcdb0 Mon Sep 17 00:00:00 2001
From: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Date: Sat, 8 Jul 2023 18:23:05 +0300
Subject: [PATCH] efi_loader: Avoid underflow when calculating remaining var
store size
The efi_var_mem_free() function calculates the available size for a new
EFI variable by subtracting the occupied buffer size and the overhead
for a new variable from the maximum buffer size set in Kconfig. This
is then returned as QueryVariableInfo()'s RemainingVariableStorageSize
output.
This can underflow as the calculation is done in and processed as
unsigned integer types. Check for underflow before doing the subtraction
and return zero if there's no space.
Fixes: f1f990a8c958 ("efi_loader: memory buffer for variables")
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
---
lib/efi_loader/efi_var_mem.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/lib/efi_loader/efi_var_mem.c b/lib/efi_loader/efi_var_mem.c
index d6b65aed12..5fa7dcb8d3 100644
--- a/lib/efi_loader/efi_var_mem.c
+++ b/lib/efi_loader/efi_var_mem.c
@@ -177,6 +177,10 @@ efi_status_t __efi_runtime efi_var_mem_ins(
u64 __efi_runtime efi_var_mem_free(void)
{
+ if (efi_var_buf->length + sizeof(struct efi_var_entry) >=
+ EFI_VAR_BUF_SIZE)
+ return 0;
+
return EFI_VAR_BUF_SIZE - efi_var_buf->length -
sizeof(struct efi_var_entry);
}
--
2.39.5