sound: Check for offset overflow in dsp_mmap_single()

Approved by:	so
Security:	FreeBSD-SA-26:27.sound
Security:	CVE-2026-45258
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation

sys/dev/sound/pcm/dsp.c

@@ -1920,6 +1920,9 @@ dsp_mmap_single(struct cdev *i_dev, vm_ooffset_t *offset,
 	struct pcm_channel *wrch, *rdch, *c;
 	int err;
 
+	if (*offset >= *offset + size)
+		return (EINVAL);
+
 	/*
 	 * https://lists.freebsd.org/pipermail/freebsd-emulation/2007-June/003698.html
 	 */

tests/sys/sound/Makefile

@@ -2,6 +2,7 @@ PACKAGE=	tests
 
 TESTSDIR=	${TESTSBASE}/sys/sound
 
+ATF_TESTS_C+=	mmap
 ATF_TESTS_C+=	pcm_read_write
 ATF_TESTS_C+=	polling
 ATF_TESTS_C+=	sndstat

tests/sys/sound/mmap.c

@@ -0,0 +1,51 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2026 The FreeBSD Foundation
+ */
+
+#include <sys/mman.h>
+#include <sys/soundcard.h>
+
+#include <atf-c.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define	FMT_ERR(s)	s ": %s", strerror(errno)
+
+ATF_TC(mmap_offset_overflow);
+ATF_TC_HEAD(mmap_offset_overflow, tc)
+{
+	atf_tc_set_md_var(tc, "descr", "mmap offset overflow test");
+	atf_tc_set_md_var(tc, "require.kmods", "snd_dummy");
+}
+
+ATF_TC_BODY(mmap_offset_overflow, tc)
+{
+	uint8_t *buf;
+	off_t off;
+	size_t len;
+	int fd;
+
+	fd = open("/dev/dsp.dummy", O_RDWR);
+	ATF_REQUIRE_MSG(fd >= 0, FMT_ERR("open"));
+
+	/* off + len will overflow and wrap back to 0. */
+	off = 0xfffffffffffff000;
+	len = 0x1000;
+
+	buf = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, off);
+	ATF_REQUIRE_MSG(buf == MAP_FAILED, FMT_ERR("mmap"));
+
+	munmap(buf, len);
+
+	close(fd);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, mmap_offset_overflow);
+
+	return (atf_no_error());
+}