From eae126f66663e5c73e5d290b8e3134449489340f Mon Sep 17 00:00:00 2001
From: Hauke Mehrtens <hauke@hauke-m.de>
Date: Sun, 4 Oct 2020 17:14:49 +0200
Subject: [PATCH] file: Check buffer size after strtok()
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This fixes a heap overflow in the parsing of the uci line.

The line which is parsed and put into pctx->buf is null terminated and
stored on the heap. In the uci_parse_line() function we use strtok() to
split this string in multiple parts after divided by a space or tab.
strtok() replaces these characters with a NULL byte. If the next byte is
NULL we assume that this NULL byte was added by strtok() and try to
parse the string after this NULL byte. If this NULL byte was not added
by strtok(), but by fgets() to mark the end of the string we would read
over this end of the string in uninitialized memory and later over the
allocated buffer.

Fix this problem by storing how long the line we read was and check if
we would read over the end of the string here.

This also adds the input which detected this crash to the corpus of the
fuzzer.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
[fixed merge conflict in tests]
Signed-off-by: Petr Štetiar <ynezz@true.cz>
---
 file.c                                        | 19 ++++++++++++++++---
 tests/cram/test-san_uci_import.t              |  1 +
 tests/cram/test_uci_import.t                  |  1 +
 .../2e18ecc3a759dedc9357b1298e9269eccc5c5a6b  |  1 +
 uci_internal.h                                |  1 +
 5 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 tests/fuzz/corpus/2e18ecc3a759dedc9357b1298e9269eccc5c5a6b

--- a/file.c
+++ b/file.c
@@ -28,6 +28,7 @@
 #include <glob.h>
 #include <string.h>
 #include <stdlib.h>
+#include <errno.h>
 
 #include "uci.h"
 #include "uci_internal.h"
@@ -63,6 +64,7 @@ __private void uci_getln(struct uci_cont
 			return;
 
 		ofs += strlen(p);
+		pctx->buf_filled = ofs;
 		if (pctx->buf[ofs - 1] == '\n') {
 			pctx->line++;
 			return;
@@ -120,6 +122,15 @@ static inline void addc(struct uci_conte
 	*pos_src += 1;
 }
 
+static int uci_increase_pos(struct uci_parse_context *pctx, size_t add)
+{
+	if (pctx->pos + add > pctx->buf_filled)
+		return -EINVAL;
+
+	pctx->pos += add;
+	return 0;
+}
+
 /*
  * parse a double quoted string argument from the command line
  */
@@ -384,7 +395,8 @@ static void uci_parse_package(struct uci
 	char *name;
 
 	/* command string null-terminated by strtok */
-	pctx->pos += strlen(pctx_cur_str(pctx)) + 1;
+	if (uci_increase_pos(pctx, strlen(pctx_cur_str(pctx)) + 1))
+		uci_parse_error(ctx, "package without name");
 
 	ofs_name = next_arg(ctx, true, true, true);
 	assert_eol(ctx);
@@ -416,7 +428,8 @@ static void uci_parse_config(struct uci_
 	}
 
 	/* command string null-terminated by strtok */
-	pctx->pos += strlen(pctx_cur_str(pctx)) + 1;
+	if (uci_increase_pos(pctx, strlen(pctx_cur_str(pctx)) + 1))
+		uci_parse_error(ctx, "config without name");
 
 	ofs_type = next_arg(ctx, true, false, false);
 	type = pctx_str(pctx, ofs_type);
@@ -466,7 +479,8 @@ static void uci_parse_option(struct uci_
 		uci_parse_error(ctx, "option/list command found before the first section");
 
 	/* command string null-terminated by strtok */
-	pctx->pos += strlen(pctx_cur_str(pctx)) + 1;
+	if (uci_increase_pos(pctx, strlen(pctx_cur_str(pctx)) + 1))
+		uci_parse_error(ctx, "option without name");
 
 	ofs_name = next_arg(ctx, true, true, false);
 	ofs_value = next_arg(ctx, false, false, false);
--- a/uci_internal.h
+++ b/uci_internal.h
@@ -33,6 +33,7 @@ struct uci_parse_context
 	const char *name;
 	char *buf;
 	int bufsz;
+	size_t buf_filled;
 	int pos;
 };
 #define pctx_pos(pctx)		((pctx)->pos)
