[ 134/167] [PATCH] efivars: Improve variable validation

Ben Hutchings
2012-05-09T05:57:36Z

From: Matthew Garrett <mjg@redhat.com>

commit 54b3a4d311c98ad94b737802a8b5f2c8c6bfd627 upstream.

Ben Hutchings pointed out that the validation in efivars was inadequate -
most obviously, an entry with size 0 would server as a DoS against the
kernel. Improve this based on his suggestions.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/firmware/efivars.c | 46 +++++++++++++++++++++++++++++---------------
1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 891e467..47408e8 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -192,18 +192,21 @@ utf16_strncmp(const efi_char16_t *a, const efi_char16_t *b, size_t len)
}

static bool
-validate_device_path(struct efi_variable *var, int match, u8 *buffer, int len)
+validate_device_path(struct efi_variable *var, int match, u8 *buffer,
+ unsigned long len)
{
struct efi_generic_dev_path *node;
int offset = 0;

node = (struct efi_generic_dev_path *)buffer;

- while (offset < len) {
- offset += node->length;
+ if (len < sizeof(*node))
+ return false;

- if (offset > len)
- return false;
+ while (offset <= len - sizeof(*node) &&
+ node->length >= sizeof(*node) &&
+ node->length <= len - offset) {
+ offset += node->length;

if ((node->type == EFI_DEV_END_PATH ||
node->type == EFI_DEV_END_PATH2) &&
@@ -222,7 +225,8 @@ validate_device_path(struct efi_variable *var, int match, u8 *buffer, int len)
}

static bool
-validate_boot_order(struct efi_variable *var, int match, u8 *buffer, int len)
+validate_boot_order(struct efi_variable *var, int match, u8 *buffer,
+ unsigned long len)
{
/* An array of 16-bit integers */
if ((len % 2) != 0)
@@ -232,19 +236,27 @@ validate_boot_order(struct efi_variable *var, int match, u8 *buffer, int len)
}

static bool
-validate_load_option(struct efi_variable *var, int match, u8 *buffer, int len)
+validate_load_option(struct efi_variable *var, int match, u8 *buffer,
+ unsigned long len)
{
u16 filepathlength;
- int i, desclength = 0;
+ int i, desclength = 0, namelen;
+
+ namelen = utf16_strnlen(var->VariableName, sizeof(var->VariableName));

/* Either "Boot" or "Driver" followed by four digits of hex */
for (i = match; i < match+4; i++) {
- if (hex_to_bin(var->VariableName[i] & 0xff) < 0)
+ if (var->VariableName[i] > 127 ||
+ hex_to_bin(var->VariableName[i] & 0xff) < 0)
return true;
}

- /* A valid entry must be at least 6 bytes */
- if (len < 6)
+ /* Reject it if there's 4 digits of hex and then further content */
+ if (namelen > match + 4)
+ return false;
+
+ /* A valid entry must be at least 8 bytes */
+ if (len < 8)
return false;

filepathlength = buffer[4] | buffer[5] << 8;
@@ -253,7 +265,7 @@ validate_load_option(struct efi_variable *var, int match, u8 *buffer, int len)
* There's no stored length for the description, so it has to be
* found by hand
*/
- desclength = utf16_strsize((efi_char16_t *)(buffer + 6), len) + 2;
+ desclength = utf16_strsize((efi_char16_t *)(buffer + 6), len - 6) + 2;

/* Each boot entry must have a descriptor */
if (!desclength)
@@ -275,7 +287,8 @@ validate_load_option(struct efi_variable *var, int match, u8 *buffer, int len)
}

static bool
-validate_uint16(struct efi_variable *var, int match, u8 *buffer, int len)
+validate_uint16(struct efi_variable *var, int match, u8 *buffer,
+ unsigned long len)
{
/* A single 16-bit integer */
if (len != 2)
@@ -285,7 +298,8 @@ validate_uint16(struct efi_variable *var, int match, u8 *buffer, int len)
}

static bool
-validate_ascii_string(struct efi_variable *var, int match, u8 *buffer, int len)
+validate_ascii_string(struct efi_variable *var, int match, u8 *buffer,
+ unsigned long len)
{
int i;

@@ -303,7 +317,7 @@ validate_ascii_string(struct efi_variable *var, int match, u8 *buffer, int len)
struct variable_validate {
char *name;
bool (*validate)(struct efi_variable *var, int match, u8 *data,
- int len);
+ unsigned long len);
};

static const struct variable_validate variable_validate[] = {
@@ -325,7 +339,7 @@ static const struct variable_validate variable_validate[] = {
};

static bool
-validate_var(struct efi_variable *var, u8 *data, int len)
+validate_var(struct efi_variable *var, u8 *data, unsigned long len)
{
int i;
u16 *unicode_name = var->VariableName;
--
1.7.10