efi_loader: limit output length for VenHw, VenMedia

VenHw and VenMedia device path nodes may carry vendor defined data of
arbitrary length. When converting a device path node to text ensure that we
do not overrun our internal buffer.

In our implementation of
EFI_DEVICE_PATH_TO_TEXT_PROTOCOL.ConvertDevicePathToText() we could first
determine the output length and then allocate buffers but that would nearly
double the code size. Therefore keep the preallocated buffers and truncate
excessive device paths instead.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

diff --git a/lib/efi_loader/efi_device_path_to_text.c b/lib/efi_loader/efi_device_path_to_text.c
index 81b8ac2..edc9fdc 100644 (file)
--- a/lib/efi_loader/efi_device_path_to_text.c
+++ b/lib/efi_loader/efi_device_path_to_text.c
@@ -67,7 +67,8 @@ static char *dp_hardware(char *s, struct efi_device_path *dp)
 
                s += sprintf(s, "VenHw(%pUl", &vdp->guid);
                n = (int)vdp->dp.length - sizeof(struct efi_device_path_vendor);
-               if (n > 0) {
+               /* Node must fit into MAX_NODE_LEN) */
+               if (n > 0 && n < MAX_NODE_LEN / 2 - 22) {
                        s += sprintf(s, ",");
                        for (i = 0; i < n; ++i)
                                s += sprintf(s, "%02x", vdp->vendor_data[i]);
@@ -251,7 +252,8 @@ static char *dp_media(char *s, struct efi_device_path *dp)
 
                s += sprintf(s, "VenMedia(%pUl", &vdp->guid);
                n = (int)vdp->dp.length - sizeof(struct efi_device_path_vendor);
-               if (n > 0) {
+               /* Node must fit into MAX_NODE_LEN) */
+               if (n > 0 && n < MAX_NODE_LEN / 2 - 24) {
                        s += sprintf(s, ",");
                        for (i = 0; i < n; ++i)
                                s += sprintf(s, "%02x", vdp->vendor_data[i]);