File 0001-yylex-Make-lexer-fatal-errors-actually-be-... of Package grub2.16181

Overview Repositories Revisions Requests Users Attributes Meta

File 0001-yylex-Make-lexer-fatal-errors-actually-be-fatal.patch of Package grub2.16181

From a948ac01744f3490fa5af4b38039f7dade68bb3e Mon Sep 17 00:00:00 2001
From: Peter Jones <pjones@redhat.com>
Date: Wed, 15 Apr 2020 15:45:02 -0400
Subject: [PATCH EMBARGOED CVE-2020-10713] yylex: Make lexer fatal errors
 actually be fatal

When presented with a command that can't be tokenized to anything
smaller than YYLMAX characters, the parser calls YY_FATAL_ERROR(errmsg),
expecting that will stop further processing, as such:

#define YY_DO_BEFORE_ACTION \
        yyg->yytext_ptr = yy_bp; \
        yyleng = (int) (yy_cp - yy_bp); \
        yyg->yy_hold_char = *yy_cp; \
        *yy_cp = '\0'; \
        if ( yyleng >= YYLMAX ) \
                YY_FATAL_ERROR( "token too large, exceeds YYLMAX" ); \
        yy_flex_strncpy( yytext, yyg->yytext_ptr, yyleng + 1 , yyscanner); \
        yyg->yy_c_buf_p = yy_cp;

The code flex generates expects that YY_FATAL_ERROR() will either return
for it or do some form of longjmp(), or handle the error in some way at
least, and so the strncpy() call isn't in an "else" clause, and thus if
YY_FATAL_ERROR() is *not* actually fatal, it does the call with the
questionable limit, and predictable results ensue.

Unfortunately, our implementation of YY_FATAL_ERROR() is:

#define YY_FATAL_ERROR(msg)                     \
     do {                                          \
       grub_printf (_("fatal error: %s\n"), _(msg));     \
     } while (0)

The same pattern exists in yyless(), and similar problems exist in users
of YY_INPUT(), several places in the main parsing loop,
yy_get_next_buffer(), yy_load_buffer_state(), yyensure_buffer_stack,
yy_scan_buffer(), etc.

All of these callers expect YY_FATAL_ERROR() to actually be fatal, and
the things they do if it returns after calling it are wildly unsafe.

Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/script/yylex.l | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/grub-core/script/yylex.l b/grub-core/script/yylex.l
index 7b44c37b7..b7203c823 100644
--- a/grub-core/script/yylex.l
+++ b/grub-core/script/yylex.l
@@ -37,11 +37,11 @@
 
 /* 
  * As we don't have access to yyscanner, we cannot do much except to
- * print the fatal error.
+ * print the fatal error and exit.
  */
 #define YY_FATAL_ERROR(msg)                     \
   do {                                          \
-    grub_printf (_("fatal error: %s\n"), _(msg));     \
+    grub_fatal (_("fatal error: %s\n"), _(msg));\
   } while (0)
 
 #define COPY(str, hint)                         \
-- 
2.11.0

Places

File 0001-yylex-Make-lexer-fatal-errors-actually-be-fatal.patch of Package grub2.16181

Places