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- From a7ab0cc98fa89a3d5098c29cbe44bcd24b0a6454 Mon Sep 17 00:00:00 2001
- From: Peter Jones <pjones@redhat.com>
- Date: Wed, 15 Apr 2020 15:45:02 -0400
- Subject: [PATCH] yylex: Make lexer fatal errors actually be fatal
- MIME-Version: 1.0
- Content-Type: text/plain; charset=UTF-8
- Content-Transfer-Encoding: 8bit
- 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>
- Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.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) \
- --
- 2.26.2
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