Merge pull request #3278 from uchiha-bug-hunter/cpio-trailer-uaf

cpio: add regression test for symlink-trailer end-of-archive check
(cherry picked from commit a6a899d655)

Makefile.am

@@ -512,6 +512,7 @@ libarchive_test_SOURCES= \
 	libarchive/test/test_read_format_cpio_svr4_gzip.c \
 	libarchive/test/test_read_format_cpio_svr4_gzip_rpm.c \
 	libarchive/test/test_read_format_cpio_svr4c_Z.c \
+	libarchive/test/test_read_format_cpio_symlink_trailer.c \
 	libarchive/test/test_read_format_empty.c \
 	libarchive/test/test_read_format_gtar_filename.c \
 	libarchive/test/test_read_format_gtar_gz.c \
@@ -936,6 +937,7 @@ libarchive_test_EXTRA_DIST=\
 	libarchive/test/test_read_format_cpio_filename_utf8_ru.cpio.uu \
 	libarchive/test/test_read_format_cpio_svr4_bzip2_rpm.rpm.uu \
 	libarchive/test/test_read_format_cpio_svr4_gzip_rpm.rpm.uu \
+	libarchive/test/test_read_format_cpio_symlink_trailer.cpio.uu \
 	libarchive/test/test_read_format_gtar_filename_cp866.tar.Z.uu \
 	libarchive/test/test_read_format_gtar_filename_eucjp.tar.Z.uu \
 	libarchive/test/test_read_format_gtar_filename_koi8r.tar.Z.uu \

libarchive/test/CMakeLists.txt

@@ -141,6 +141,7 @@ IF(ENABLE_TEST)
     test_read_format_cpio_svr4_gzip.c
     test_read_format_cpio_svr4_gzip_rpm.c
     test_read_format_cpio_svr4c_Z.c
+    test_read_format_cpio_symlink_trailer.c
     test_read_format_empty.c
     test_read_format_gtar_filename.c
     test_read_format_gtar_gz.c

libarchive/test/test_read_format_cpio_symlink_trailer.c

@@ -0,0 +1,58 @@
+/*-
+ * Copyright (c) 2026 Kaif Khan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#include "test.h"
+
+/*
+ * The cpio reader reads an entry's name into a read-ahead buffer and holds
+ * that pointer to compare the name against "TRAILER!!!" (end of archive).
+ * For a symlink entry the link body is read first, and a large body can grow
+ * (and free) the read-ahead buffer, leaving the name pointer dangling before
+ * the trailer comparison.
+ *
+ * The reference archive is a single newc entry: a symlink named "TRAILER!!!"
+ * with a 128 KiB body.  Reading it in small blocks assembles the name in the
+ * reader's copy buffer, which the symlink body read then reallocates; the
+ * trailer must still be detected without touching freed memory.
+ */
+DEFINE_TEST(test_read_format_cpio_symlink_trailer)
+{
+	const char *name = "test_read_format_cpio_symlink_trailer.cpio";
+	struct archive_entry *ae;
+	struct archive *a;
+
+	extract_reference_file(name);
+
+	assert((a = archive_read_new()) != NULL);
+	assertEqualIntA(a, ARCHIVE_OK, archive_read_support_format_cpio(a));
+	/* Small block size so the name is assembled in the reader's copy
+	 * buffer, which the symlink body read then reallocates. */
+	assertEqualIntA(a, ARCHIVE_OK, archive_read_open_filename(a, name, 13));
+
+	/* The "TRAILER!!!" entry ends the archive. */
+	assertEqualIntA(a, ARCHIVE_EOF, archive_read_next_header(a, &ae));
+
+	assertEqualIntA(a, ARCHIVE_OK, archive_read_close(a));
+	assertEqualInt(ARCHIVE_OK, archive_read_free(a));
+}