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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Wed, 15 Apr 2020 15:45:02 -0400
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Subject: [PATCH] yylex: Make lexer fatal errors actually be fatal
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When presented with a command that can't be tokenized to anything
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smaller than YYLMAX characters, the parser calls YY_FATAL_ERROR(errmsg),
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expecting that will stop further processing, as such:
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#define YY_DO_BEFORE_ACTION \
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yyg->yytext_ptr = yy_bp; \
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yyleng = (int) (yy_cp - yy_bp); \
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yyg->yy_hold_char = *yy_cp; \
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*yy_cp = '\0'; \
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if ( yyleng >= YYLMAX ) \
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YY_FATAL_ERROR( "token too large, exceeds YYLMAX" ); \
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yy_flex_strncpy( yytext, yyg->yytext_ptr, yyleng + 1 , yyscanner); \
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yyg->yy_c_buf_p = yy_cp;
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The code flex generates expects that YY_FATAL_ERROR() will either return
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for it or do some form of longjmp(), or handle the error in some way at
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least, and so the strncpy() call isn't in an "else" clause, and thus if
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YY_FATAL_ERROR() is *not* actually fatal, it does the call with the
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questionable limit, and predictable results ensue.
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Unfortunately, our implementation of YY_FATAL_ERROR() is:
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#define YY_FATAL_ERROR(msg) \
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do { \
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grub_printf (_("fatal error: %s\n"), _(msg)); \
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} while (0)
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The same pattern exists in yyless(), and similar problems exist in users
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of YY_INPUT(), several places in the main parsing loop,
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yy_get_next_buffer(), yy_load_buffer_state(), yyensure_buffer_stack,
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yy_scan_buffer(), etc.
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All of these callers expect YY_FATAL_ERROR() to actually be fatal, and
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the things they do if it returns after calling it are wildly unsafe.
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Fixes: CVE-2020-10713
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Signed-off-by: Peter Jones <pjones@redhat.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Upstream-commit-id: 926df817dc8
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---
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grub-core/script/yylex.l | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/grub-core/script/yylex.l b/grub-core/script/yylex.l
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index 9c2cfe11531..a3f15dfe571 100644
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--- a/grub-core/script/yylex.l
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+++ b/grub-core/script/yylex.l
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@@ -37,11 +37,11 @@
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/*
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* As we don't have access to yyscanner, we cannot do much except to
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- * print the fatal error.
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+ * print the fatal error and exit.
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*/
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#define YY_FATAL_ERROR(msg) \
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do { \
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- grub_printf (_("fatal error: %s\n"), _(msg)); \
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+ grub_fatal (_("fatal error: %s\n"), _(msg));\
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} while (0)
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#define COPY(str, hint) \
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