Buffer overflow in drivers/xen/sys-hypervisor.c

commit 27fdbab4221b375de54bf91919798d88520c6e28 upstream.

The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is
neither NUL terminated nor a string.

The first causes a buffer overflow as sprintf in buildid_show will
read and copy till it finds a NUL.

00000000  f4 91 51 f4 dd 38 9e 9d  65 47 52 eb 10 71 db 50  |..Q..8..eGR..q.P|
00000010  b9 a8 01 42 6f 2e 32                              |...Bo.2|
00000017

So use a memcpy instead of sprintf to have the correct value:

00000000  f4 91 51 f4 dd 00 9e 9d  65 47 52 eb 10 71 db 50  |..Q.....eGR..q.P|
00000010  b9 a8 01 42                                       |...B|
00000014

(the above have a hack to embed a zero inside and check it's
returned correctly).

This is XSA-485 / CVE-2026-31786

Fixes: 84b7625 ("xen: add sysfs node for hypervisor build id")
Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

Author: jgross1

drivers/xen/sys-hypervisor.c

@@ -366,15 +366,19 @@ static ssize_t buildid_show(struct hyp_sysfs_attr *attr, char *buffer)
 			ret = sprintf(buffer, "<denied>");
 		return ret;
 	}
+	if (ret > PAGE_SIZE)
+		return -ENOSPC;
 
 	buildid = kmalloc(sizeof(*buildid) + ret, GFP_KERNEL);
 	if (!buildid)
 		return -ENOMEM;
 
 	buildid->len = ret;
 	ret = HYPERVISOR_xen_version(XENVER_build_id, buildid);
-	if (ret > 0)
-		ret = sprintf(buffer, "%s", buildid->buf);
+	if (ret > 0) {
+		/* Build id is binary, not a string. */
+		memcpy(buffer, buildid->buf, ret);
+	}
 	kfree(buildid);
 
 	return ret;