| From a4d3fbdff1e3ca8f87642af2ac8752c30c617a3e Mon Sep 17 00:00:00 2001 |
| From: Peter Jones <pjones@redhat.com> |
| Date: Wed, 15 Apr 2020 15:45:02 -0400 |
| Subject: 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. |
| |
| Fixes: CVE-2020-10713 |
| |
| Signed-off-by: Peter Jones <pjones@redhat.com> |
| Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com> |
| |
| Upstream-Status: Backport [https://git.savannah.gnu.org/cgit/grub.git/commit/?id=a4d3fbdff1e3ca8f87642af2ac8752c30c617a3e] |
| CVE: CVE-2020-10713 |
| Signed-off-by: Chee Yang Lee <chee.yang.lee@intel.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) \ |
| -- |
| cgit v1.2.1 |
| |