From 7425d421340594f50c717ff7129b6ee71280a447 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20=C5=A0tetiar?= <ynezz@true.cz>
Date: Mon, 9 Dec 2019 15:27:16 +0100
Subject: blob: fix OOB access in blob_check_type
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Found by fuzzer:

 ERROR: AddressSanitizer: SEGV on unknown address 0x602100000455
 The signal is caused by a READ memory access.
     #0 in blob_check_type blob.c:214:43
     #1 in blob_parse_attr blob.c:234:9
     #2 in blob_parse_untrusted blob.c:272:12
     #3 in fuzz_blob_parse tests/fuzzer/test-blob-parse-fuzzer.c:34:2
     #4 in LLVMFuzzerTestOneInput tests/fuzzer/test-blob-parse-fuzzer.c:39:2

Caused by following line:

	if (type == BLOB_ATTR_STRING && data[len - 1] != 0)

where len was pointing outside of the data buffer.

Signed-off-by: Petr Štetiar <ynezz@true.cz>
---
 blob.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

--- a/blob.c
+++ b/blob.c
@@ -218,20 +218,33 @@ blob_check_type(const void *ptr, unsigne
 }
 
 static int
-blob_parse_attr(struct blob_attr *attr, struct blob_attr **data, const struct blob_attr_info *info, int max)
+blob_parse_attr(struct blob_attr *attr, size_t attr_len, struct blob_attr **data, const struct blob_attr_info *info, int max)
 {
+	int id;
+	size_t len;
 	int found = 0;
-	int id = blob_id(attr);
-	size_t len = blob_len(attr);
+	size_t data_len;
 
+	if (!attr || attr_len < sizeof(struct blob_attr))
+		return 0;
+
+	id = blob_id(attr);
 	if (id >= max)
 		return 0;
 
+	len = blob_raw_len(attr);
+	if (len > attr_len || len < sizeof(struct blob_attr))
+		return 0;
+
+	data_len = blob_len(attr);
+	if (data_len > len)
+		return 0;
+
 	if (info) {
 		int type = info[id].type;
 
 		if (type < BLOB_ATTR_LAST) {
-			if (!blob_check_type(blob_data(attr), len, type))
+			if (!blob_check_type(blob_data(attr), data_len, type))
 				return 0;
 		}
 
@@ -285,7 +298,7 @@ blob_parse(struct blob_attr *attr, struc
 
 	memset(data, 0, sizeof(struct blob_attr *) * max);
 	blob_for_each_attr(pos, attr, rem) {
-		found += blob_parse_attr(pos, data, info, max);
+		found += blob_parse_attr(pos, rem, data, info, max);
 	}
 
 	return found;
