efivars: Improve variable validation

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>

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 150e4ec98485404481e1413bec14012882af4f3f..0535c219046de1f98f64c30682fa71e8449debed 100644 (file)
--- 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;