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efivars: Improve variable validation

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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>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Garrett 2012-05-03 16:50:46 -04:00 committed by Linus Torvalds
parent fec6c20b57
commit 54b3a4d311
1 changed files with 30 additions and 16 deletions
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46
drivers/firmware/efivars.c
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@ -192,19 +192,22 @@ utf16_strncmp(const efi_char16_t *a, const efi_char16_t *b, size_t len)
} }
static bool 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; struct efi_generic_dev_path *node;
int offset = 0; int offset = 0;
node = (struct efi_generic_dev_path *)buffer; node = (struct efi_generic_dev_path *)buffer;
while (offset < len) { if (len < sizeof(*node))
offset += node->length;
if (offset > len)
return false; 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 || if ((node->type == EFI_DEV_END_PATH ||
node->type == EFI_DEV_END_PATH2) && node->type == EFI_DEV_END_PATH2) &&
node->sub_type == EFI_DEV_END_ENTIRE) node->sub_type == EFI_DEV_END_ENTIRE)
@ -222,7 +225,8 @@ validate_device_path(struct efi_variable *var, int match, u8 *buffer, int len)
} }
static bool 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 */ /* An array of 16-bit integers */
if ((len % 2) != 0) if ((len % 2) != 0)
@ -232,19 +236,27 @@ validate_boot_order(struct efi_variable *var, int match, u8 *buffer, int len)
} }
static bool 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; 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 */ /* Either "Boot" or "Driver" followed by four digits of hex */
for (i = match; i < match+4; i++) { 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; return true;
} }
/* A valid entry must be at least 6 bytes */ /* Reject it if there's 4 digits of hex and then further content */
if (len < 6) if (namelen > match + 4)
return false;
/* A valid entry must be at least 8 bytes */
if (len < 8)
return false; return false;
filepathlength = buffer[4] | buffer[5] << 8; 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 * There's no stored length for the description, so it has to be
* found by hand * 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 */ /* Each boot entry must have a descriptor */
if (!desclength) if (!desclength)
@ -275,7 +287,8 @@ validate_load_option(struct efi_variable *var, int match, u8 *buffer, int len)
} }
static bool 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 */ /* A single 16-bit integer */
if (len != 2) if (len != 2)
@ -285,7 +298,8 @@ validate_uint16(struct efi_variable *var, int match, u8 *buffer, int len)
} }
static bool 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; int i;
@ -303,7 +317,7 @@ validate_ascii_string(struct efi_variable *var, int match, u8 *buffer, int len)
struct variable_validate { struct variable_validate {
char *name; char *name;
bool (*validate)(struct efi_variable *var, int match, u8 *data, bool (*validate)(struct efi_variable *var, int match, u8 *data,
int len); unsigned long len);
}; };
static const struct variable_validate variable_validate[] = { static const struct variable_validate variable_validate[] = {
@ -325,7 +339,7 @@ static const struct variable_validate variable_validate[] = {
}; };
static bool 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; int i;
u16 *unicode_name = var->VariableName; u16 *unicode_name = var->VariableName;