From 07b94e27afafebf31ef3cd868866a1e383750086 Mon Sep 17 00:00:00 2001
From: Milan Crha <mcrha@redhat.com>
Date: Mon, 19 May 2025 17:48:27 +0200
Subject: [PATCH] soup-multipart: Verify array bounds before accessing its
 members

The boundary could be at a place which, calculated, pointed
before the beginning of the array. Check the bounds, to avoid
read out of the array bounds.

Closes https://gitlab.gnome.org/GNOME/libsoup/-/issues/447
---
 libsoup/soup-multipart.c |  2 +-
 tests/multipart-test.c   | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/libsoup/soup-multipart.c b/libsoup/soup-multipart.c
index 102ce372..e1c442ec 100644
--- a/libsoup/soup-multipart.c
+++ b/libsoup/soup-multipart.c
@@ -104,7 +104,7 @@ find_boundary (const char *start, const char *end,
 			continue;
 
 		/* Check that it's at start of line */
-		if (!(b == start || (b[-1] == '\n' && b[-2] == '\r')))
+		if (!(b == start || (b - start >= 2 && b[-1] == '\n' && b[-2] == '\r')))
 			continue;
 
 		/* Check for "--" or "\r\n" after boundary */
diff --git a/tests/multipart-test.c b/tests/multipart-test.c
index f5b98688..d1f7425c 100644
--- a/tests/multipart-test.c
+++ b/tests/multipart-test.c
@@ -527,6 +527,27 @@ test_multipart_bounds_bad (void)
 	g_bytes_unref (bytes);
 }
 
+static void
+test_multipart_bounds_bad_2 (void)
+{
+	SoupMultipart *multipart;
+	SoupMessageHeaders *headers;
+	GBytes *bytes;
+	const char *raw_data = "\n--123\r\nline\r\n--123--\r";
+
+	headers = soup_message_headers_new (SOUP_MESSAGE_HEADERS_MULTIPART);
+	soup_message_headers_append (headers, "Content-Type", "multipart/mixed; boundary=\"123\"");
+
+	bytes = g_bytes_new (raw_data, strlen (raw_data));
+
+	multipart = soup_multipart_new_from_message (headers, bytes);
+	g_assert_nonnull (multipart);
+
+	soup_multipart_free (multipart);
+	soup_message_headers_unref (headers);
+	g_bytes_unref (bytes);
+}
+
 int
 main (int argc, char **argv)
 {
 
-- 
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