efi/libstub: Don't parse overlong command lines

Check if the command line passed in is larger than COMMAND_LINE_SIZE,
and truncate it to the last full argument if so.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200521002921.69650-1-nivedita@alum.mit.eduSigned-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/efi-stub-helper.c

@@ -9,10 +9,12 @@
 
 #include <stdarg.h>
 
+#include <linux/ctype.h>
 #include <linux/efi.h>
 #include <linux/kernel.h>
 #include <linux/printk.h> /* For CONSOLE_LOGLEVEL_* */
 #include <asm/efi.h>
+#include <asm/setup.h>
 
 #include "efistub.h"
 
@@ -217,22 +219,33 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
 	unsigned long cmdline_addr = 0;
 	int options_chars = efi_table_attr(image, load_options_size) / 2;
 	const u16 *options = efi_table_attr(image, load_options);
-	int options_bytes = 0;  /* UTF-8 bytes */
+	int options_bytes = 0, safe_options_bytes = 0;  /* UTF-8 bytes */
+	bool in_quote = false;
 	efi_status_t status;
 
 	if (options) {
 		s2 = options;
-		while (options_chars--) {
+		while (options_bytes < COMMAND_LINE_SIZE && options_chars--) {
 			u16 c = *s2++;
 
-			if (c == L'\0' || c == L'\n')
-				break;
+			if (c < 0x80) {
+				if (c == L'\0' || c == L'\n')
+					break;
+				if (c == L'"')
+					in_quote = !in_quote;
+				else if (!in_quote && isspace((char)c))
+					safe_options_bytes = options_bytes;
+
+				options_bytes++;
+				continue;
+			}
+
 			/*
 			 * Get the number of UTF-8 bytes corresponding to a
 			 * UTF-16 character.
 			 * The first part handles everything in the BMP.
 			 */
-			options_bytes += 1 + (c >= 0x80) + (c >= 0x800);
+			options_bytes += 2 + (c >= 0x800);
 			/*
 			 * Add one more byte for valid surrogate pairs. Invalid
 			 * surrogates will be replaced with 0xfffd and take up
@@ -253,6 +266,11 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
 				}
 			}
 		}
+		if (options_bytes >= COMMAND_LINE_SIZE) {
+			options_bytes = safe_options_bytes;
+			efi_err("Command line is too long: truncated to %d bytes\n",
+				options_bytes);
+		}
 	}
 
 	options_bytes++;	/* NUL termination */